An aquaintance says that a suitably baited old-fashioned mousetrap works womders. You may want to weaken the spring a little, (he says) - you wouldn't want to break the dear creature's nose, would you? Once it's been sprung, just leave it in view. The cat will give it a very, very, wide berth, or hopefully stay off your property altogether! (Of course, I would never use such a dastardly device myself). Oh. And please, please, don't ever use it if you have any hedgehogs around.