The neighborhood cats have turned our backyard into giant litter box

I would probably have a long chat with my neighbors , their are some cute signs about no popping in yard unless you want it returned as my gift to you ! 🐈 Good luck !

Start by telling your neighbor, and showing her the cat feces, all over your property. Tell her it's unsanitary for that stuff to be there and not cleaned up. It's a health hazard, and it's an invitation for other cats to use your yard as well. It's hard to tell a neighbor this, it causes bad feelings, which you try to avoid. If the problem is not rectified, call the health department if nothing else works.

Put chilli powder or cayenn pepper in the garden. It doesn't harm the cates but does "nip" their noses if they sniff it. They soon learn to avoid your garden. You can also buy an ultrasonic speaker from amazon that keeps cats, dogs etc away from the area. They hear it but we cant

contact local Animal Control; if stray cats, have them removed; if owned cats and no 'leash law' for cats ( there usually isn't), talk to you attorney -- would be a civil matter, but a law suit might get their attention -- and if they say they don't own the cats -- then trap and take to animal shelter - DO NOT!! just turn them loose somewhere else.

Place mothballs where you know they frequent. Cats also hate aluminum foil. Cover dirt and weigh down with rocks. Hopefully this will discourage them after time and you can remove deterrents.

You may need to put up a fence. cats can climb some fences but it will at least slow them down. If they go to specific areas in your yard like your garden or a kid's sandbox, you can just focus on making those areas as unpleasant for them as possible. here is a site with more ideas: http://wildlifeanimalcontrol.com/straycats.html

Put some mothballs around and chicken wire in your garden, they do not like to walk on this.