Cayenne pepper sprinkled around the beds you don't want used.

& keep a spritzer bottle of water handy just in case you see them "thinking about" it.

Put a sprinkler on a motion detector.

If you can, get some chicken wire screen and lay pieces on the surface of the new flower bed and box garden. That will make it difficult for the cats to dig holes, which will make it less fun to poop there. Cover with a light layer of mulch to disguise the screen.

Cats don't like the smell of citrus, so shredded citrus peelings scattered around the beds would also be a deterrent.

I wonder if there's any way you'd consider keeping the kitties indoors a larger portion of the day.

Please don't ever use cayenne pepper to ward off animals. For cats it's even more harmful since they bathe themselves. A cat licking its paws and then washing its eyes will make for a painful experience.........and not one that they will relate to the garden.