Welcome to PT. I also recently had some urine marking and inappropiate peeing problems. I have 6 cats and I had to add 3 more litterboxes. I also bought some cat attract litter. I added it on top of the old litter that I had been using and it worked right away. You can buy this at Petsmart or many place online.
I've also been using the feliway plugins and spray for almost 3 months now and it has helped a lot. My oldest is the alpha cat and he has some aggression problems so he's now on an herbal supplement that I hope will work for him. I tried him on the clomicalm but he eventually became immune to it so it didn't work any more. You may also want to ask your vet about prozac. Good luck. I know how frustrating this situation can be.