Ok, so it is early minutes (he's been in there about half an hour), but it seems to be working.
DH spent his afternoon at work fashioning slots - they have been screwed into the door frame and our second gate slotted in. He even thought to put in a pin so that He Of Great Strength couldn't just lift the gate up and off.
I can't take photos, batteries dead at the moment but I'll get some up tomorrow hopefully.
He isn't asleep, he is still having the odd yell, but the frenzy of being shut in completely has gone.
Hurrah!
How long before he works out how to climb over the top and splats the high drop on the other side?