The main problem with all the ideas is that you have a cat of your own. Our little cat scarcely left the house and never really went further than the back garden. Every other cat that came in the garden seemed to beat her up. She was hopeless, though, as a feline and seemed to think of herself as a human baby.
You are right Slid this has been the problem thankfully it seems to have almost stopped using our yard now so I guess it's doing it elsewhere.