Easy, Get a dog, or borrow one for a few days. once a cats been seen off by a dog it avoids that garden like the plague. I have two neighbours cats that drive me mad, they climb the trees in my garden and take the baby birds, sit in the field at the end of the garden and stalk pheaseants, then dig up the FRONT garden and poo everywhere. now, after the dog episode, they will not walk past my house, they cross the road then come back over to a neighbours garden.
I am an animal friendly person, but these cats ( brother and sister) are thrown out each morning to do whatever cats do all day, and obviously they don't do it in their own garden.
Annie.