This reminds me of the episode of My Cat from Hell that was just on this past weekend. Jackson (the "cat whisperer") put a can of air that shoots a small blast of air when it detects movement in front of it. It doesn't hurt the cat, just startles them and eventually they should stay away from the area.
Now, don't ask me where you can get this motion sensored canned air. I have NO clue!

But it sounds like you may have already come upon a solution.