First I would suggest going to the Vet's also. Sounds more like a behaviorual problem.

Yoshi was put on Ritilan, the cat version. He was having problems with marking his terratory....often. It took 3 months, but it is working.

The Feliaway plug-in I just used when we went away for vacation, and it did seem to help. Before we left I checked the entire house for "markings" with a black-light. There were none, when we came back, I checked again. Much to my surprise, there weren't any!! So I guess between the medication and the Feliway it worked!!