“After being “conditioned” by the zaps, most dogs never venture beyond the perimeter....” We had a totally crazy but very dear pointer-setter mix. He kept breaking out of the yards to go on jaunts through the neighborhood. As a last resort, we got an invisible fence. He would sit as near the fence as he could tolerate until he drained the battery. Then, somehow, he’d chew any of the exposed wire and break the circuit in as many places as possible. He drove me bonkers, LOL! I still miss him.
Your dog definitely tricked out the system.
OMG....tough dog.
Those zaps *hurt*.