We used to use a scat mat. It was very effective until Onyx peed on the battery pack. It was turned off at the time, so it didn't hurt Onyx, but the scat mat is dead!

Not we use SSSSSCAT Spray. It's basically a can of compressed air. There is a motion detector on the top of the bottle. When it senses movement it emits a high pitch squeal, if the cat doesn't leave, it lets out a blast of compressed air. Doesn't hurt the cat at all, but it's very effective. We leave ours set to just make the noise now and it still works.