Mishi started not using the litterbox for a bit too after Mitzi kept rebuffing his attempts at affection. I bought some of that "Nature's Miracle" stuff and it seems to have worked to take the scent out. Then I moved his litterbox to where he was leaving his messes for me to clean up. It seems to have worked -- now they're BOTH using that litterbox and Mitzi is being a little bit nicer with the big goon. They still aren't snugglers, but at least she lets him lick her occasionally.