Also we used a product called simple solution for our new rescue dog but there is also one for cats.
Basically it is hard (as you know) to get rid of the smell of urine/faeces and this product contains enzymes to destroy the smell. This results in the cat being less likely to return and mark the same spot.
On the plus side we have just done three weeks without any indoor accidents. In these challenging times it is good to celebrate small victories!