Place an apricot on a seesaw which, when the cat removes the apricot, swings down and knocks a lever that makes a blade cut a rope that releases a guillotine with a match attached. When the guillotine falls, the match rubs down a piece of sandpaper (tied to a stuffed aardvark of course - I once tried a sloth but an aardvark is best), which then lights a fuse that ignites a candle that burns through a string, releasing a swinging boot that kicks a water-filled balloon that squirts water down a tube and sprays at the cat. Certainly works for me. Oh and the answer to the clue is 'dayboard' (it's a kind of board you carry around during the day, as opposed to a nightboard).