How long did he use it before the trouble started? If he was using it and suddenly stopped, I would probably want to rule out potential health issues. Has Binoo been to the vet for a check up lately? Maybe bring him in to get looked at, make sure he doesn't have a UTI or something like that that would alter his litter box habits.
Have you tried high sided litter pans? They make them for cats so they don't pee over the side of the box, but many people use them for rabbits as well.
Have you tried high sided litter pans? They make them for cats so they don't pee over the side of the box, but many people use them for rabbits as well.