Although this could be a urinary infection, it is more likely to be completely harmless. Balanoposthitis (I confess to having to check the spelling) - infection of the prepuce, is very common in young dogs. It usually self cures and frequently recurs. Treatment of mild cases is not needed. I'd only treat if there was inflammation or difficulty urinating. If you are taking him, then take a urine sample - ideally no more than an hour or so before the appointment.