Is he spraying rather than just peeing? Mine did that when a new cat came into the neighbourhood and Shadow (14)realised he was not "boss cat" anymore. Try Feliway which you can get from the vet in either spray or plugs. Shadow even did it in electric sockets! Also you can get stuff to put on his paws which he will lick off, from Helios Pharmacy in Tunbridge Wells 01892 537254 - they send it by post. Might be worth a try as these things have a calming effect and the spraying is caused by stress. Even females do it sometimes. Hope this helps.
Sheann