A friend doesn't smell her indoor ferrets anymore... I've worked at a shelter, I'm pretty much used to all animal smells but ferrets are really bad and on bad days it makes me feel sick. Her whole house smells like ass. (In the US ferrets often get descented, in Europe not). With cats it already helps a lot to really wash your litter box at least once a week and wash the floor around it daily. Obviously depends on what cleaners you use, should be something that neutralizes odor.