I put one in when I got Rupert.
Apparently they don't work for German Shepherds. He figured out if he ran fast enough he only got shocked for a split second. The flags pointed out what to jump over. We called the manufacturer and got a collar with more voltage. It didn't stop him either. He just took the shock. The fence worked,I know because I tried it out. Put my thumb between the electrodes on the collar and got within range. It hurt up to my shoulder.
I talked to a state police k9 officer and said those don't work for German Shepherd Dogs and the Malinois. He said they're too smart and will take some pain. I had to train him to stay within the boundaries of our property. I just let him out and he patrols the perimeter.
Groot doesnt eat trees does he? Rupert gave up on bonsai after his elm died.