Gypsy is right about the invisible fence. It works -- and it doesn't. If a dog for any reason bolts, it not only passes through to the outside of the fence (beyond it's effectiveness) and makes it impossible (except by bolting into the yard--unlikely) that it will return to the safety of your yard.

This, in its own way "trains" the dog that just a split second of discomfort will result in freedom--a choice he's going to be more and more willing to take.

Another problem with invisible fences---other animals, wild and otherwise, have free access to your yard and pets, jeopardizing their safety.

I have seen many happy users of the IF though.