how long has this been going on? Why don't you want him neutured? is he champion in shows or conformation class you'll be putting him in? Is he a rare breed? Can't handle medical procedure? These are the only reasons not to have him neutered. If he started it when he was 5-6 months old, it is becoming habit, the reason he doesn't pee sometimes is because he is empty at that moment. He doesn't see you as alpha, and he is telling any available female he is ready and any male he has claimed area. Once he marks he goes back and replenishes his smell when he smells that it is getting weaker. Covering it doesn't do any good, you need to remove it, with an enzymatic cleaner like Nature's Miracle. You have to teach him it is not acceptable to do this in YOUR territory. I can't put a complete answer on here to help you...go to
http://orangedog.forumup.com/index.php?mforum= orangedog
go to "general Advice" and read "Nothing in life is free", that is a start and then go to Behavior and read Potty training this will give you tips. You say he isn't left on his own and doesn't have free run then how is he taking the 5 seconds to: stop, smell, get in position and squat or lift his leg and pee? Someone is not watching..if you got a dog YOU know is doing this then he needs constant watching, don't take your eyes off him, so you can stop it in the act and take him out IMMEADIATELY, this is what you have to do. Read the advice on the website, and ask questions if you'd like.