I don't think they had invisible fence back in my dog's day.
Scares the crap out of me when I'm out walking and loose dogs come tearing at you right to the edge of the road.
They seem cool though. All the neighborhood kids loved my dog and vice versa. We lived on a quiet dead end street. He would've loved sitting at the edge of our yard while they were out playing ball and whatnot. He was a a big dopey Samoyed/Lab mix. I don't think the shock through all that fur would've phased him enough to keep him in the yard.
I couldn't trust him with anyone in a uniform though. He had a habit of pinning the meter man against the wall in our garage. (Who was dumb enough to open a garage door with a big Beware of Dog sign on it).
The cops came to our house because my brother's car died and was left somewhere. My dog wouldn't let the cop get out of the car. He didn't bite or growl ...... he just put his big paws on the windows and told the uniformed stranger that he should stay where he was.