Pet Guardian system? Has anyone used it?

The only time I would rely on an underground fence is if I was outside with the dog to make sure it did it's job. I would not trust the dog out there by itself. There are far too many dangers that an invisible fence cannot protect against. Such as, it will not stop people or other animals from stepping on your property, which what if someone was bitten or what if another dog attacked yours? Plus, there may be a temptation for the dog to leave that is stronger than the mild shock he would get. It's just not a good idea to depend solely on that. I do think they are a great tool to ist you in training the dog not to leave the yard so they can play out there with you.