In my never ending quest to keep squirrels from spending the day eating every last sunflower seed I've tried many non-lethal approaches. I thought the fence charger was the ultimate, but the little bastards ran right over the charged copper plate. I think I saw them wearing rubber boots.
My latest idea was introducing sound to startle them. It worked for a while, then one brave squirrel realized that it was just noise. After that they just mocked me.
Anyway I was proud of my design. I used an ancient bank alarm bell, a "wall-wart" transformer, a remote control for Christmas lights and a weather proof enclosure.