But, I haven't been able to locate one of those either.
I currently have an electric fence. I have had one for 28 years. I had no dogs with high prey. I had a collie who ran from one side of the yard to the other, barking at cars, but did not cross the line.
I currently have a 87 lb German Shepherd dog that I have trained on the fence from oohlalapets.com and their best rated invisible dog fence. He was taught with flags and shock, like a puppy where, so to speak, lines were drawn. Even if his collar is off, he does not leave the yard. Remember that he is low-energy and weak-loving. I was looking for a breeder who breeds in these qualities. He is also an old-fashioned GSD with a straight back as they are spawned.