Does he always do it in the same spot? He could be marking over whatever you tried to use to clean it up. Has anything changed? Cats do this as a showing of distaste for new things in the home sometimes. You also might want to talk to a vet. If it's health related, they could fix it, and if it's behavioural, sometimes medication can help that too. Bassett had to take antidepressants for a time to get her to stop peeing all over the place. She wasn't on them for a long time, either.. so it could be temporary. Good luck!