Puzzled re keeping DS (3) safe at night

[Bug2014]

Hi,
DS is 3 and very tall and since he's been in his own room he has had a stair gate on the door to keep him from going downstairs and wandering about the house getting into (dangerous) mischief at night. Soon he will either work out how to open the stair gate, or manage to climb over it, so we will have to remove it.
I am puzzled about what happens when we do- he is not really safe to use the stairs on his own yet, and obv by no means safe to have unsupervised access to the whole house if he gets up while we are asleep. What do people do in this situation? Just get a taller stair gate? Although he usually wakes us up instantly on waking by shouting from his room, I am concerned that he may wander about quietly at night without waking us, and come to some harm. It would be impossible to make the whole house completely safe for him, every night.
Any enlightenment appreciated!

[QTPie]

Greyslates, depends where you put it. We had a landing at the top of our stairs and could set the stairgate 5/6ft back from the actual top of the stairs.