We have had this problem, and dealt with it by lying in wait for the Evil Neighbor Cat and squirting it with a squirt gun. You put a little bit of vinegar into the water in the gun—it won't hurt the cat; it was a vet who suggested that to me, so I'm sure it isn't harmful. We did that a few times, and the cat never came back. Unfortunately, *other* neighbor cat's did, and we had to repeat the exercise. ...All I can say is that my life is pretty plain.