We also have two cats. We were having problems with them peeing and puking, and we got the Feliway diffuser thing. It looks kind of like a Glade plug-in, and it supposedly releases pheromones to make cats feel happy. It was kind of expensive, but SO worth it! They haven't peed on anything (and we just bought a house, so we were freaked that they would pee everywhere), and our one anxiety-ridden puke-y cat throws up so much less now.
Anyway, just wanted to recommend Feliway. :) Give it a try. I hope it works. I know cat pee smell is wretched. :)
This definitely intrigued me! So I decided to look it up.
I found a helpful FAQ about Feliway on this site. I was going to copy-paste, but I decided it would be better to just point you to the site and suggest you read it yourself if you're interested. It explains everything in good, easy-to-understand detail.
It is interesting reading about Feliway. They claim that it not only will help with urinating outside the litter box, but also will stop cats from fighting. This especially intrigues me, because Lewis and Ebony fight all the time. My last two cats (Koko and Yum Yum) were so cuddly and friendly with each other that it makes me said that Lewis and Ebony seem to dislike each other.
Does anyone else have experience with Feliway? Anyone know of a good place to buy it? I would like to look into it further, but I definitely think this might be an answer for us! It's like with acne treatments - you get to the point where you'll just try anything! I'll see if the vet has any recommendations when I go on Saturday.