Feral Cat Using Fallow SFG for cat box

Hi all - I didn't clear out or even care about my SFG boxes after last summer since I was long-haul sick and didn't have the energy so just I just ignored it. However, I did acquire a big feral cat in July as a solution to the rats who were eating my tomatoes and grapes.  I think he has done a good job keeping the rats at bay.  Now I am feeling better and I want to clean up my boxes and start a new garden.  Yesterday I observed that Dexter, my cat, has been using my two 4 x 4 boxes as his catbox, probably for months now.

I'm pretty sure I have read that one should never use domestic animal droppings in the SFG boxes or in any food-producing garden. I have no idea how to rehabilitate my boxes and then, how to keep Dex out of them.       Has anyone else had this problem?  Is there a way to remedy this or do I have to move?

also if you have a establish or portable grid in place they will not use it.

Apparently the Japanese (or is it Chinese?) take the cat problem very seriously. My SO got me this handy garden cat deterrent:


It's really too nice to use! Makes a better conversational piece. Also, there's almost no room for anything to grow!

I try to keep in perspective that thanks to the 3.5  feral cats that visit my yard, I haven't had any rodent problems the last few years. Still, they seem to love to use the box whenever I've just planted stuff. My working solution is a "fort" of spikes around the newly planted items, leaning out at an angle. Cat lovers, please note that I have the blunt side up, not the sharp side:



Once plants start growing above 6 inches, the cats don't bother them, thankfully.

Last year I even tried putting out cat litter so the cats would have a "real" bathroom. Apparently they didn't like the decor since it never got used.

Whenever I've installed a new "tulle" shed or agribon barn, it gets attacked at least once by some cat. Possibly because they want to climb up it, and it takes them a couple tries to learn that that doesn't work.

you do have a challenge

I have gotten into the habit of wearing gloves because of the neighbor's cat and the raccoons. Nothing like finding a surprise "Tootsie Roll" while digging for carrots and onions