I have found that Marshall Ferret Bi-Odor Waste Deodorizer that you add to the ferrets water works great. It eliminates the odor before it starts. I have used it when I have had as many as 6 ferrets. I now have 3 and the cat smells worse than they ever did. I purchase it in a 32 oz. bottle and it lasts for a long time even adding it every day. [Posted in FML issue 4752]