Do you feel he's getting enough nap time during the day? Is he overtired at bedtime? I found that our son who is 15months old was waking for 2 hours in the night because he was overtired and not getting enough sleep. We started putting him to bed a little earlier at night and that solved the problem. If he did wake at night this is what we did:
-go in and do pd, say night night - and we left the room
-we were finding that staying in the room made him more awake and he thought we were there to play, even if we were constantly doing pd
-so we would walk out/walk in and pd - he was really upset when we would leave the first couple times but eventually he would lay down even before we made it to his crib.
- we would wait outside his door and give him 10 sec. to settle, if he stopped crying, we would not go in or if he started to cry again, we would go in and do the same thing
-our son thought that pd was play so we began walk out/in - this let him know we were serious about going back to sleep and also we are not in the room with our son when he does go to sleep so this reinforced him going back to sleep on his own
-at first this took 1hour plus but now if it happens it only takes 5 min.
-when we put him to bed a ltitle earlier, the problem went away
Good luck