Hi Alicia, here are a few things you can try - https://www.wikihow.com/Keep-Cats-Out-of-a-Garden
Motion sensor sprinklers.
I agree with Kelli, when the cats approach where you don't want them, a hose attached to a motion sensor sprinkler will spray them...and they do not like to be wet. Very soon they will learn to avoid your property.
Hello Alicia: One thing you can try is to put down a layer of lava rocks. They come in a couple of colours. They are pretty and the cats don't like walking on them, let alone digging in them to do their business. And, as a bonus, if someone decides that they want to walk through the area at night, you will hear them crunching on the rocks. Good luck
Try moth balls
Hi Alicia, sounds like a great idea, I planted cacti in my flower bed where they were pooping, it is so smelly and gross to clean up, it has helped, with the pooping cats, but the bunnies can still sleep on the flower bed under the bushes.
Put out fragrances that keep cats away.
Scatter fresh orange or lemon peels. Wet coffee grounds—which you may be able to get for free from coffee houses and fast food chains—and metal pans filled with vinegar also deter cats. an out-of-the-way spot in your yard. Clean the area frequently.
Plantings of ruta graveolens (Rue), lemon balm, lavender, rosemary, peppermint can be effective. Soak cotton balls in tea tree oil and lemon or orange essential oils and place them where cats are a problem.