Cats used to use the house plants instead of the litter box - so we used a plant mister on "stream" and also HISSED dissaprovingly (SSST)! They got the idea with the verbal addition a lot faster.

I had read using sycamore balls to mulch works but that won't do unless you have a tree.

So what about trying the other repellent - oyster grit. Iit's used for slugs because it's sharp and unpleasant to crawl/walk on.

Should work for cats too. You're smart enough to use a knee-pad or shoes.

Luck! E.