It really depends on the dog. In Wyoming I had 4 foot fencing and not a problem with the dogs - it was an acre and they got a walk in the morning and a walk at night and knew it. In Arkansas, I lived in town. I had 6 ft privacy fencing on the top part of the property and 4 ft chain-link on the rest. No problem with dogs jumping the fence. Other dogs will scale or jump a 6 foot fence.