In the movie Grumpy Old Men, John goes up on Max's roof and starts spraying his roof with water on top of the snow. So supposedly water goes to the bottom of the snow, freezes and sets up an ice sheet. Any vibration that occurs from a door closing the snow avalanches down. I can see this working with a metal roof but with a shingled roof, IDK. "Gotta use hot water, ya putz." Anybody pull a prank like this on somebody?