Few answers! Try anything citrus. Lemon rind etc. I dont know if you can buy some sort of citrus spray. Prevention is better than the cure. As said in a previous response, cover the ground. A newly raked bed or plot might as well have a neon sign.

Buy a male cat. Cats never leave anything in their own garden. If you have a male they will also spray to mark their territory,(spelt wrong i think) which will deter other cat's.

If your lucky enough to have a big garden, plant some catnip in an unused corner. Bears around a honey pot, flys round s**t, rubber neckers at a crash etc etc.