They don't hold up well to snow at all. That's how Daisy started coming over to our yard! A few inches of snow provided enough insulation that she didn't feel the shock at all and began to wander at will. My dogs chewed her collar off her and her owner has never bothered to get another one.

I wouldn't trust an invisible fence for a second with my dogs. I've never met a husky who wouldn't just walk right through the shock if there was something more interesting on the other side. I have met many who couldn't be bothered to get shocked again on their way home and ended up lost!

I never worried about things coming into my yard either. The odd loose dog wasn't a problem. Until the night a wolf came through and tried to kill my dogs. That wolf took 22 dogs out of my subdivision in four months. Took almost six months and a monsterous vet bill to get Hobo back on his paws. We fenced four acres after that, seven feet high, reinforced on the bottom to prevent digging out, double gates across the driveway--the peace of mind was and still is worth every dime.