At the risk of being indelicate, I had a sporadic problem one time with my cats peeing on the bathroom rug by the toilet. Upon investigate it was discovered that the male human in our family had "splashed" on the rug while using the toilet leaving a scent behind that just could not be ignored and had to be dealt with by the cats in their own fashion. For my part, I got the rug off the floor and it became a nonissue then.
In your situation, I would definitely suspect something is going on with the urinary tract. Also, is there a new cat in the neighbourhood perhaps? If it's a tom and he's coming around your yard and leaving his mark on the outside of your house that may be upsetting your boy.
Last edited by Chevaux; 04-08-2013 at 08:39 PM.