I'm looking for ideas, currently I've got him contained on a chain in a small 1z-level high 5x5 building with pillars on the corners and drawbridges for walls. The idea is to open the walls when attacked on the surface and let him nuke the area but I imagine there's better uses.

I assume the training he's gotten from my legendary animal trainer will eventually fall off and he'll be fully aggressive so I don't think I'll have the luxury of moving him later very easily.

Also- LOL @ a 400 year old dragon the size of a bus with fire breath hotter than the sun stuck in a wooden cage.

EDIT: Update in comments.