So leave the fence on 24/7; maybe they'll find a restaurant in a better neighborhood. If you leave it off much, they'll know it; I think they can smell it when it's on, and know the difference. No juice, no protection; that's why it's there, isn't it?
It is most definitely on 24/7. The only time it's off is when I'm working in the run. I constantly check it to make sure.