So you already have a PetSafe Wireless Pet Containment System to make your pets behave? The Petsafe Invisible Radio Controlled Dog Fence lets you expand containment size for your pets. You can cover an area up to 1/2 acre. You get 5 adjustable levels of correction. The device lets you add an unlimited number of dogs with the extra wireless fence receiver collar. Just plug the transmitter into an electrical outlet close to the area where you want to contain your pet, and you are set. Not cheap but useful for folks who want to take better care of their pet.
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