I do talks on how to develop wildlife habitats for backyards. There are indeed some forms of wildlife you don't want. They are often deterred by simply laying chicken wire flat on the garden beds. Most animals that have soft pawpads are deterred from continuing to use that area or dig in that area. I use the technique to deter raccoons from digging up freshly planted flower bulbs.
Most cats don't potty in the open. It is generally under or behind a bush. If your neighbor has an accumulation of mulch or leaves at the base of bushes or trees it should be racked away. No digging compound...no potty alfresco!
One last option is to use a citrus spray. This of course would need to be applied after every rainfall. Contrary to what others may say about using different urine odors, cats are territorial and use their urine and feces to mark what they think is theirs. I might ask is Sweet Pea a male or female?
I see a lot of folks telling you to keep Sweet Pea inside. Some cats do accomadate to the situation very well...others though become escape artists.
This solution is coming from a fellow pet sitter who recently did a sit for a client who has this system. She was totally impressed with it.
Female. And I’m looking into that Spray Motion Deterrent