No ideas really Jean - you don't have cats do you? If they sleep on the bed it might make him mark it. I'll be interested in responses to this though as Alfie has peed on my sofa a couple of times recently. In fact the cover for one of the cushions is drying on the radiator just now as he did it on Sunday when I nipped out to Tesco
He, too, only does it when I'm not there and I know it's him as well from the smell. This is the third time he's done it now and it's a bit odd, not to mention annoying! Thank god the throw I have on the sofa has a waterproof backing so the damage is never too bad but I'd still rather he didn't do it!