Try to rule out anything physically wrong with him with your vet.
I'd definatly be crating him at night and when you can't watch him. We'll put a leash on puppies and hook it to our belt, so they have to follow us everywhere. I'd also get on a schedule for feeding, walking and taking him outside to do his business.
Take him for a walk everyday as well, it may help his metabolism, needing more water, and moving his bowls at more appropriate times.
Also, do you allow him to feed through out the day or does he get fed only once or twice a day? I would only feed twice a day, half portions for a daily amount. This will also regulate BMs.
And finally, I'd make him earn everything he does, including attention, food etc... make him do some obedience before you put his bowl down, make him sit and wait to eat until you tell him too. Keep him off furniture etc.. If he doesn't have any physical or mental health issues, he might just be doing it cause he can.
good luck!