I had a problem with a very large dog pooping all over my front yard. I bought this very expensive and very stinky citronella and garlic formula to spray on the grass to make the area undesirable to the dog. Didn't work.
They sell coyote and wolf urine, etc., but I moved away before I tried that stuff.
You could also put up a little chicken wire fence for a few weeks until the cats get in the habit of going elsewhere, and then take it down.