We have many annoying feral cats that invade our backyard. As well as ruthlessly beheading and disembowelling possums, they have really loud fights - it's like a women's tennis match is going on at 3 am. I have thought of cashing on this violence by dressing them up in little silky shorts and gloves and having cat UFC. I worry they would scratch the crap out of me while I was trying to do this though. With my cat allergies my eyes would probably get really itchy too.
Instead I am thinking of revisiting one of my old ideas and getting a little boy pissing fountain. The fountain would have a motion sensor and when cats came in to the yard the boy would swivel to the appropriate angle and release a squirt the appropriate distance to piss all over the cat. It would be brilliantly entertaining.