That made me laugh. 🙂
I have 2 cats here too... but they are somehow polite enough to stay off my computers, one likes to sit on my wacom tablet though.
It's rather difficult to get them to stop doing something once they enjoy it.
iAlertU is certainly worth a try.
Or put iTunes in front so that space starts the music, max the volume and make it play something like Slayer, then again, your cat looks like he likes heavy metal. 🙂