try the air-hose bomb. You drill a 2 liter plastic bottle to accept a air fitting. Hook it up to a airline and slip the bottle under the car he's working near. Just crack the air line open a hair and sit back and wait. Makes a nice loud boom. Will scare the crap out of him.

Jim T

"Every normal man must be tempted at times to spit upon his hands, hoist the black flag, and begin slitting throats".--H.L. Mencken Bumper sticker, OXYMORON #65 - Liberal Thinker