ours works great with our two mutts (jack russel mix and dalmation/australian shepherd mix). training is key; i remember coming across a tip that when you first put flags out to mark the boundary, leash your dogs when they approach. if they try to bolt across the wire, pull them back. that way they don't learn that the shock will stop. our big dog is quite protective of his yard, but will not even try to cross the line, even if other animals are approaching.