Posted: 19/12/2012 at 18:27
This is why I unashamedly advocate making cats' lives as unpleasant as possible - short of physical violence. Scare them in any way you can: throw things towards them, shout or hiss at them, stare at them until they begin to lose confidence and then run or throw at them, make sudden loud noises, whatever else you can think of.
They do learn whose territory it is, and I have had no cats in my garden for years despite all the surrounding houses having at least one cat. It took about three months to become cat-free, with hardly any effort.