Cats just eat grass outdoors. They won't mess with anything else. Although Aconite looks like grass and is deadly toxic. Aconitum, known as aconite, monkshood, wolfsbane, leopard's bane, women's bane, Devil's helmet or blue rocket. It's toxic enough that you shouldn't handle the plant with your bare hands. But it sure doesn't seem to hurt the squirrels, who eat Aconite plants anyway. Not that I would miss a squirrel or two, maybe the Aconite eaters are gone now. My suggestion; plant catnip in somebody else's yard. Far enough away to keep them out of your yard. Fox, bobcat, or coyote urine sometimes works also, as a repellent. But that would probably attract fox, bobcat and coyotes, lol. Note: historical lessons learned the hard way over and over again, say that getting rid of feral cats results in rats and mice. The first sign of rats and mice is a bunch of hawks and falcons hanging around staring at the yards. Which isn't good for any remaining cats, because hawks like cats also.