Once cats get it into their minds that somewhere is a loo stopping them is a real challenge. Don't leave any bare earth is the first thing, cover with grit or bark - not composted bark though. Or stick twigs in the ground basically you have to make it difficult for the cats to dig their little holes.

I have had terrible trouble keeping animals away from my new plantations! Dogs and cats!

In raised beds, it's easy! Buy some chicken wire or small gauge fencing grill. Cut to shape of bed, in sections if nec, and peg down just above the surface of the bed. Ease the plants through til they're going on their own, or, cut around the plants.

Cats can't scrape...and dogs can't run through!

Try it, it works!