Cats are pure evil. That's why I like them. Though I wouldn't own one.
If you're going to take pot-shots at them, bear in mind that they're classified under law as wild animals, not vermin. Wild animals harming/maiming/killing/torturing other animals is not illegal. Humans harming/maiming/killing/torturing animals is quite harshly dealt with.
Until someone comes up with a domestic animal, classified under law as a wild animal, that eats cats (or the law changes) - you're stuck.
I find a super-soaker, and mowing orange peel into the lawn quite effective against keeping cats away.