Chain length should be considered in relationship to anchoring method and reduction of injury to the animal (lunge injuries). The shorter the chain the lower the possibility for injury (in all cases multiple swivels are needed). When using ridgid stakes you must take into account the animals ability to "pump" the stakes out by standing over the stake and rearing upward. For coyotes 16" too 18" of chain will prevent pumping. For cable staking systems (earth anchors) pumping is not an issue and 8" total chain plus 3 swivels works nicely.
