I don't think I would *ever* let my dog outside in a wire fence unsupervised. My fear is that there is no block against other dogs. So if another dog decides that MY dog looks like lunch, my dog can't run away.

However, my brother & sister in laws have a shepherd mix that is trained BEAUTIFULLY!! The system works flawlessly for them. She was older when they started training her as well. So we are thinking of trying it as it is so we can fence in our entire yard. But like I said, I would never leave him unsupervised for any lenght of time.