You say you 'put him out' but I suspect you don't go with him to make sure he does something besides sniff around. Maybe a short walk would help. On a leash, around the perimeter of the yard should be enough.

Then limit his access to the house at night. Either a crate to sleep in (next to your bed, maybe) or a short leash attached to your bed. He may wake you up for a few nights to go out, but these trips should diminish quickly when he realizes he's still going to be contained for sleep.

I'm assuming he's seen a vet to rule out diabetes. A soaked bed was the only clue with my dog. He managed to get outside during the day, but not at night.