Where's a moderator when you need one.

I knew a guy who didn't like the cats messing his front yard so hooked a motion sensor to his sprinklers. I also heard those ultrasonic dog barking stoppers bother cats (it doesn't affect their barking). You could, with a lot of wire, connect a motion sensor or a sensative car alarm to an ultrasonic widget or windsheild washer to keep them away.