We have a conventional fence here for our guys, but one of our neighbors uses an invisible fence for their little dog. (He looks like a gray Norwegian elkhound/akita type dog, but is small, about the size of a beagle.) Anyway, they leave him out in the yard when they go to work, and several times he has shown up at our house while the owners are gone. Recently, when we were going for a walk with my big guys, we heard this awful, blood curdling scream, and saw him charging down the hill toward the road, screaming all the way down. All I could figure was that he got zapped crossing the fence line, but it wasn't enough to deter him from doing so. Of course, since he got zapped while leaving the yard, he refused to go back in, and it was several hours before his owners got home, so he was running loose the whole time. The last time I saw him, he had one rear quarter shaved, and a huge scar from apparent surgery- not sure what happened, would not be surprised if he had been hit by a car, but the owners still depend on the invisible fence thing while they are away.