Cats are territorial they’ll always desecrate in your garden. Chances are your soil hasn’t been turned over and is hard so they go for the easy option, the lawn.
Accepting the fact you’ll get cat shite regardless, best to redirect the cat shite to a more appropriate area.
Dig a hole at the back of the garden, behind a bush, behind the shed, somewhere out of sight, large as you like, or dig a couple of holes, if you want to really go to town chuck a bit of cat litter in them. (not essential but faster results) Cats love defecating in holes, and will scratch the surrounding soil to cover it over too! Once every few months turn the soil over.
This will take you from poo minefield, to zero poo. Try it.