mohtballs do the trick, kept them away from my garden for months. you can buy them from wilko's very cheap in laundry section. just scatter around your borders or in soil but make sure no childen pick them up. hope this helps
May I just point out that, contrary what bazwillrun says, shooting cats is illegal and will result in prosecution. Why do people like that bother to post answers?
Well said markasus. Even with a patrolling terrier we cannot keep the wrens safe, nor the bank voles in the rockery. Though I deprecate cruelty to cats or any other animal!