From Martha Stewart concerning a musty smelling book: suggestions contributed by the Northeast Document Conservation Center in Andover, Massachusetts, and Glenn Horowitz Booksellers in East Hampton and New York City. Both our experts agree that there is no guaranteed way to remove the musty smell of old books, but you can try by first wiping your book with a clean, soft, barely damp cloth. Wipe off the cover, the top of the pages, and the pages themselves. If the mildew contains any moisture, open up the book and leave it in a sunny, airy place to dry. A fan will help speed up this process. Then fill the bottom of a large garbage can with odor-absorbing material such as kitty litter, charcoal, or baking soda. Kitty litter is the most inexpensive of the three. Place the book in a smaller can, and place this can inside the larger one. Cover the large can and let it sit, checking the progress of the book every several days. If all goes well, your book will be ready for reading within a month.

Try a closed tub with kitty litter? I hate when this happens!

Thank you so much for your responses. Someone recommended zinsser shellac seal coat wax free (sanding sealer) before applying the polyurethane. I dont know if it'll work because as you mentioned the urine may have penetrated in between the boards into subfloor but we don't have the time and money to replace anything now. I guess if by next year the smell persists we will remove the hardwood floor and replace it. When the AC is on it doesn't smell, but if the AC is off for a while the odor is there. It is not very strong but enough that it bothers us.

I never have an issue with garbage smells spreading to the rest of my cabinetry unless (A) I haven't taken the trash out (I typically don't go longer than 24 hrs., 36 max), or (B) I haven't washed the garbage bin itself recently. The plastic garbage bin can really hold onto odors, even if you have nothing smelly in there currently. Try washing the plastic bin out with Ajax powder, give it a good scrub, let dry. I also use my disposal a lot. I made sure to get a 3/4 hp Waste King which is powerful with a lot of torque. I even put chicken bones down there. I agree with the other poster who said even if you install some kind of metal shield, you will still get hit with the odor when you open the garbage pull-out. So those shields take care of the symptom, not the underlying cause. As I said, scrub the bin out, use the disposal, and take out the garbage with more frequency.