I have been throwing water over cats since I moved in and we very rarely get them back after that. A glass of water usually works but if there is a stubborn one that hold it's ground then they get the hose treatment. Cat people may not agree with me but cats hate it and a drop of water isn't harmful. I have also put orange and lemon peel around my fences which deters them as well. Again, cat people will shout at me as I think citrus is toxic to cats but from the evidence I have I don't see it as a problem as the cats near me that have sniffed it have just walked away straight away in disgust.