I have a 10 mth male apoo that still has potty issues. I use a diaper for him at night, any suggestions?

He will be nuetered tomorrow. Has access to outdoors. Only pet. We take him out after meals, sleep, before bed, and when we get home, he will potty. He still wets/marks during the night which is why he wears a belly band. Only has two meals/day, but water available to him until 7:00 p.m. He has gone through 3 rounds of puppy cles.