When I was in college, my friend's cousin had a problem with a neighborhood cat that would sit on his warm car during the night. He had a pet scorpion, and one night he left it on the roof of his car secured by a string. Apparently, he and his friends waited and watched for the cat to arrive. And when it did, it did what any curious animal does. It crawled up to the strange thing with the six legs and long tail on the roof and put its nose right up to it. The next thing the guys saw was the limp cat sliding off the roof. It sounds like a made up story to me since most scorpions don't have instant kill powers, but maybe the small size of the cat relative to an adult human had something to do with it. Hell, if Steve-O from Wild Boyz can take two scorpion stings in a row on his bare ass, why can't a cat take one on the nose?
My friend here at work told me his brother had a similar problem with a cat sitting on his car. He used a slightly different method. He left a small bowl filled anti-freeze on the hood of the car as a treat. It's known that ethylene glycol can kill small animals. He never had a cat problem again.
I have an even more demented idea. Get a bottle of "Jumbo-Gro" plant grow formula and feed it to a canary, then place the all-growed-up little fellar by your amp. There's nothing funnier than the sight of a dog-sized canary putting a cat in a leglock! Obviously I watch too much Tex Avery cartoons.