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A retractable animal tether, comprising a hand-held support; a spool rotatably mounted on the support; and a flexible cord wound on the spool, said flexible cord having an end which is connected to the spool and a second end which may be connected with the animal. The application of a first force F1

A retractable animal tether, comprising a hand-held support; a spool rotatably mounted on the support; and a flexible cord wound on the spool, said flexible cord having an end which is connected to the spool and a second end which may be connected with the animal. The application of a first force F1 to a free end of the flexible cord causes a portion of the flexible cord to unwind from the spool. The tether also includes a means for preventing the remainder of the flexible cord from unwinding from the spool unless a second force F2 is applied to the free end of the flexible cord, said force F2 being greater than said force F1.

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1. A retractable animal tether, comprising:a) a support; b) a spool mounted on the support, said spool being rotatable; c) a leash wound on the spool; and d) at least one spring having a variable cross-sectional area and being configured to provide variable resistance to rotation of the spool, where

1. A retractable animal tether, comprising:a) a support; b) a spool mounted on the support, said spool being rotatable; c) a leash wound on the spool; and d) at least one spring having a variable cross-sectional area and being configured to provide variable resistance to rotation of the spool, wherein an effective spring constant of said at least one spring changes as the spool rotates. 2. The device of claim 1, additionally comprising a braking means, wherein activation of said braking means prevents unwinding of the leash from the spool.3. The device of claim 2, wherein said braking means acts independently of said at least one spring.4. The device of claim 3, wherein said at least one spring activates automatically, providing increased resistance to rotation of the spool as a defined portion of the cord is unwound from the spool; and wherein said braking means is activated by a user and stops rotation of the spool to prevent unwinding of the leash from the spool.5. The device of claim 1, wherein the at least one spring comprises a first spring having a spring constant K1 and a second spring having a spring constant K2, where K2 is less than K1.6. The device of claim 1, wherein the at least one spring comprises a single spring having a variable spring constant.7. The device of claim 6, wherein the spool is rotatably mounted on a nonrotatable axle, and the spring having a variable spring constant comprises a spirally coiled spring having an inner end which is rigidly connected to the axle, and an outer end which is rigidly connected with the spool at a predetermined radial distance from the axle;wherein the spring has a first portion and a second portion, wherein said first portion of said spring has a spring constant K2; and said second portion of said spring has a spring constant K1, wherein K1 is either constant or variable; wherein K2 is less than K1. 8. The device of claim 7, wherein the first portion of the spring comprises a plurality of inner coils having a spring constant K2, and the second portion of the spring comprises at least one outer coil having a spring constant K1.9. The device of claim 7, wherein the spring has a first portion having a constant spring constant K2, a second portion having a constant spring constant K1, and a third intermediate portion having a non-constant spring constant K3.10. The device of claim 9, wherein the non-constant spring constant K3 changes in a stepwise fashion.11. The device of claim 9, wherein the non-constant spring constant K3 changes in a gradual fashion.12. The device of claim 7, wherein the coiled spring is manufactured from a first strip of metal of constant thickness, said first strip of metal having a first portion and a second portion; and a second strip of metal of constant thickness; said second strip of metal being fastened to the second portion of the first strip of metal.13. The device of claim 12, wherein a plurality of second strips of metal of constant thickness is fastened to the second portion of the first strip of metal.14. The device of claim 1, wherein the at least one spring comprises a plurality of springs.15. The device of claim 14, wherein the spool is rotatably mounted on a nonrotatable axle, and the at least one spring comprises at least two springs which are coiled together; said at least two springs comprising a first spirally coiled spring having an inner end which is rigidly connected to the axle, and an outer end which is rigidly connected with the spool at a predetermined radial distance from the axle; and a second spirally coiled spring which is shorter than the first spirally coiled spring, said second spirally coiled spring having an outer end which is rigidly connected with the outer end of the first spirally coiled spring.16. The device of claim 15, wherein rotation of the spool initially applies tension on said first spirally coiled spring, wherein said first spirally coiled spring has a spring constant K2; and wherein continued rotation of the spool subsequently applies tension on both said first spirally coiled spring and said second spirally coiled spring, wherein said first spirally coiled spring and said second spirally coiled spring act as a single spring having an effective constant spring constant K1;wherein K2 is less than K1. 17. The device of claim 1, wherein said at least one spring having a variable cross-sectional area comprises:a) a single-layered spring having a variable cross-sectional area; or b) a multilayered spring, where a thick portion of the multilayered spring has a greater number of layers than a thin portion of the multilayered spring. 18. The device of claim 17, wherein said multilayered spring comprises:i) a multilayered spring comprising at least a first layer and a second layer, said first layer and said second layer being laminated together; or ii) a multilayered spring comprising at least a first spring and a second spring, wherein said first spring and said second spring are able to flex independently. 19. A retractable animal tether, comprising:a) a support; b) a spool mounted on the support, said spool being rotatable; c) a leash wound on the spool; and d) a single spirally coiled spring having a variable effective spring constant and being configured to provide variable resistance to rotation of the spool, wherein said variable effective spring constant increases as the spool rotates so as to unwind the leash; wherein the coiled spring is manufactured from a strip of metal, said strip of metal having a variable cross-sectional area. 20. A retractable animal tether, comprising:a) a support; b) a spool rotatably mounted on the support; c) a leash wound on the spool, said leash having a first portion having an end which is connected to the spool, and a second portion having a free end; and d) at least one spring having a variable cross sectional area, said spring applying a variable resistance to rotation of said spool; wherein the at least one spring prevents the second portion of the leash from unwinding from the spool unless a first force F1 is applied to the second portion of the leash; and wherein the at least one spring prevents the first portion of the leash from unwinding from the spool unless a second force F2 is applied to the first portion of the leash, said force F2 being greater than said force F1. 21. The device of claim 20, additionally comprising a braking means, wherein said braking means prevents unwinding of the leash from the spool.22. The device of claim 20, wherein the at least one spring comprises a first spring and a second spring, said first spring having a spring constant K1, wherein tension is applied to said first spring by rotation of the spool while said first portion of the leash is unwinding, but not while the second portion of the leash is unwinding.23. The device of claim 22, wherein said second spring has a spring constant K2, wherein tension is applied to said second spring by rotation of the spool while said second portion of the leash is unwinding, where K2 is less than K1.24. The device of claim 23, wherein said first spring and said second spring comprise separate portions of a single spring having a variable spring constant.25. The device of claim 20, wherein the at least one spring comprises a single spring having a variable spring constant.26. The device of claim 25, wherein the spool is rotatably mounted on a nonrotatable axle, and the single spring having a variable spring constant comprises a spirally coiled spring having an inner end which is rigidly connected to the axle, and an outer end which is rigidly connected with the spool at a predetermined radial distance from the axle;wherein the spring has a first portion having a spring constant K2, and a second portion having a spring constant K1, where K2 is less than K1. 27. The device of claim 26, wherein the spring has a first portion having a spring constant K2, a second portion having a spring constant K1, and a third intermediate portion having a non-constant spring constant K3.28. A retractable animal tether, comprising:a) support; b) a spool rotatably mounted on the support; c) a leash wound on the spool, said leash having a first portion having an end which is connected to the spool, and a second portion having a free end; and d) at least one spring having a variable spring constant, said spring applying a variable resistance to rotation of said spool; wherein the at least one spring prevents the second portion of the leash from unwinding from the spool unless a first force F1 is applied to the second portion of the leash; and wherein the at least one spring prevents the first portion of the leash from unwinding from the spool unless a second force F2 is applied to the first portion of the leash, said force F2 being greater than said force F1; wherein the spring has a first portion having a spring constant K2, a second portion having a spring constant K1, and a third intermediate portion having a non-constant spring constant K3; wherein the coiled spring is manufactured from a strip of metal, said strip of metal having a variable cross-sectional area. 29. The device of claim 28, wherein the coiled spring is manufactured from a first strip of metal of constant thickness, said first strip of metal having a first portion and a second portion; and a second strip of metal of constant thickness; at least one end of said second strip of metal being fastened to the second portion of the first strip of metal.30. A device for retractably holding a cord, comprising:a) a housing; b) an axle rigidly mounted in the housing; c) a spool having an inner surface and an outer surface rotatably mounted on the axle, wherein the inner surface of the spool is spaced from the axle; d) a flexible cord wound on the outer surface of the spool, said cord having a first end which is rigidly connected to the spool and a second end which extends through a passage in the housing; and e) a spirally coiled spring having a variable spring constant, said spring having a first end which is rigidly connected to the axle, and a second end which is rigidly connected to the inner surface of the spool; said first end of said spring having a lower spring constant than said second end of said spring; wherein the spring exerts a variable resistance to rotation of the spool. 31. A retractable animal tether, comprising:a) an axle; b) a spool mounted on the axle, said spool being rotatable; c) a leash wound on the spool; and d) at least one spring acting between said spool and said axle, said at least one spring having a first end connected to said axle and a second end connected to said spool, said first end of said at least one spring having a lower spring constant than said second end of said at least one spring; wherein said at least one spring provides variable resistance to rotation of the spool.