Perhaps you may find this site helpful:
http://thescaredycat.com/whats-the-b...cat-repellent/
I know irresponsible cat owners are annoying. I love cats and am the proud mommy of one but he doesn't go outside because of the dangers others present to him i.e. poisonous repellents, cars, etc.
We are here to protect animals, all animals so if all you want to achieve is for them to not take up residence in your yard, natural repellents are worth a try and are highly effective. I've helped my mother in law with the same advice. Also, you can buy lion poop online and apparently that repels cats and other feral animals. Mother in law swears by it and the proceeds often go to conservation efforts.