When you consider some of the horrible alternatives, a shock collar doesn't seem that bad. We've all heard of dogs hanging themselves by there collars when trying to go over fences. And once they're out of the fence, there are even more dangers.

If you cant be there to watch all the time, you can use an invisible fence system. You would run the wire along your existing fence. There is a long training process when using an invisible fence system and you must take the time to follow it, but when done correctly these systems work great.