Please tell me that :-
a. He won't be up and down the stairs once I put him to bed.
and
b. That I won't spend the entire night lying awake listening for the slightest creak and hint that he might be heading down the stairs (or even falling down them!!!!) 
He's 2.6. Usually (with the rare exception) stays in bed once he's put there.
DH is away for 10 days so no chance of me fixing it. 