Hi I have a persian who does this. When i asked vet about it he said it was anxiety related. When we looked back at when it happens he only seems to do it when something different has happened or im not around. He came in and peed in hall a couple of days ago and we had not had any problems even going away and leaving him over night which would normally upset him but they have started building next door and he doesnt like the noise. I have also got his brother there is 4 months between them and we have no problems with snowy wetting any were. Have you noticed he does it when something or someone different has been / happened could be that. I have a feliway plug in which has helped alot with roony that was his first accident in months might be worth giving your vet a ring and asking there advice.