My daughter use to have ferrets and sometimes training is not so simple! They are fast little buggers, and when you have more than one it can be a handful to litter box train them! She use to put a triangle litter box in every corner of her room to help them to figure it out (when they were outside of their multi-level cage). It became pretty hopeless though; they just weren't consistent with the location of their poopage!!
Ah well........................