Shadow peed outside the litter box for a month straight when we lived in Tucson. We could not figure what the matter was with her so we had to put a litter box by the front door where she was urinating. We took her to the vet, figured out it wasn't a UTI and he asked some general questions. It turned out that I had moved the litter box from the large bathroom to the small bathroom and she did not like it being moved. I put a litter box back and she quit peeing on the floor.

We are currently living in AL and she started peeing outside the box again. ON her favorite beds to boot. Her brother started attacking her more so I figured this was her way to "get revenge" but took her to the vet to rule out UTI, Diabetes, whatever. Again, it was behavioral and the best solution we came up with was to simply separate the two while we are gone and at night. This has worked amazingly well (knock on wood) and she has her own litter box that no one else uses unless Callie "spends the night" in our room. She is no longer in fear of being attacked, she prefers the bedroom over anywhere else in the house and Whisper's aggression has ceased now that they are only together while we are home. We have had no accidents and she has regained some adorable behaviors she had lost years ago (like pouncing on things moving under the covers and she is a lot more loving now).

I would try and rule out any UTIs but it sounds like this is more behavioral than anything. You should try putting a litter box in both the bathroom and the bedroom--as you should have a litter box for each cat + 1. I would try to steam clean the carpets with Pet Carpet Rinse and Nature's MIracle also works wonders. Good luck!