How to repeal cats from using my garden as theur bathroom?

https://davidsuzuki.org/queen-of-green/keep-cats-garden/

several options... depending on where you live, call 'Animal Control' to come remove the cats; use a 'SCRAM' product for deterring dogs/cats/deer, etc. from flower/gardens; plastic forks (the white picnic ones ) pushed handle down into the ground work great for bunnies, squirrels and (sometimes) cats!

This kind of falls under the guise of “if you can’t beat them, join them.” Instead of trying to stop them entirely, designate an area the size of a litter box and set it up just for them. you can make it cute and a bit fancy or super simple, but if you can guide them to a place that is there’s, then they are more likely to avoid the rest of your garden. Example: designate your area, dig down about 6-8 inches, smooth it out. Fill with the following layers. 1 lg. bag of pea gravel, then 1 lg bag of charcoal (pet store). Top off with sand or non-clumping kitty litter. For the fancy, surround 3 sides with a mini fence and/or plant large clumps of kitty litter all around. Voilà.

*theirs

spray vinegar, works every time