[the chi]

Hmmm, put up a sign in your yard for a few days, maybe a week. On it I'd say something like:

ATTN CAT OWNERS

I will begin trapping and relocating any cats found defecating and destroying my lawn. If you have cats, please consider keeping them inside to avoid any confusion/missing cats.

if you are on friendly terms with any of your neighbors, Id give them a personal heads up, but you are well within your rights to do whatever you want on your property and you've given the cat owners fair warning. If you trap and remove their cat, it becomes their fault for not obeying the laws. Most places leash laws pertain to cats too and they are in violation by not restricting their cats. If they pee on your car, I'd recommend electrifying the rims and metal pieces.

Problems like yours are the reason I dont believe in having outside cats in a city. At this point Im considering antifreeze and prime rib for the neighbors dogs...however they sleep later than I do so I am finding that letting my girls out at 5am is almost as disruptive to them as their dogs barking all day, evening and after Im already in bed trying to sleep.