I would have to agree with the BB gun. Get ya a little scope on it and immerse yourself in the world of Sniping!! Here kitty kitty kitty... POP.... MEEEEEEOOOOOOWWWWW!!!!!! Problem solved.
Wow thats alot of ways to kill a cat. Well I know a Great Dane would prob. keep em out, I had two of them along time ago and the only thing they couldnt keep out of the yard was this huge wild bore....