You know what does work? Hunted To Extinction, or more accurately, in the case of these vermin man-made cats, hunted-to-extirpation.

It worked where I live! The eradication of hundreds and hundreds of these vermin cats by shooting and burying every last one I saw (collared or not, because stray collared cats are the very source of every last feral cat, was so complete and effective that I've not seen even ONE cat in over 8 years now in the whole area. (So much for that "vacuum effect" LIE of yours, eh?) Cat-lickers finally learned their well-earned and much-deserved lesson at long-last. They don't DARE let any of their vermin roam free anymore. To do so means their cat dies within hours of its release. Is that what it's going to take to teach all of you? YEP! You're all just that phenomenally ignorant, stupid, and criminally irresponsible.

Let the shooting begin. And don't stop until every last cat is gone from your area. It's the ONLY thing that works. Guaranteed.