You have gotten some great advice- I had problems with my boys marking- and alot of times it seemed they'd do it when I wasn't paying enough attention to them- like if I had friends over. Also, when I added a 2nd male it became worse, as it was a dominance issue.

Definitely get the belly band, and the suggestions for the odors are good- other things that have always worked great for me for potty odors are Oxyclean and plain white vinegar.