and the dog will never approach the fence again.

And by “shock” I mean at a very low intensity. It’s more of an unpleasant surprise than a painful shock.

Most animals, especially dogs, learn very quickly.

I understand your position. I do. But each owner needs to weigh the downside of the collar to the harm if the dog gets loose. We had 2 dogs who either scaled an 8’ fence, dug under it, or chewed through the wood planks to get out. Then they were off and crossing busy roads. One dog was trained after 1 shock; the second took 3.