this sounds mean, but when he pees, put his nose in it....i know but it worked with my pup....
also, put a bell on the door (like a chime or something), so everytime you take him outside to do his business he will hear the sound.....make sure your always take him out of that door........be patient, when time goes on, take his paw and knock the bell with it....then EVENTUALLY he will ring the bell himself