Got a nice place, in a flat V between a pair of mountains. A bit of iron, no flux, only 40 deep. Just finished digging out the frame of the safe room, built in preparation for the king once he arrives. Any dangerous creature, like as dragons and such, will be stored just before his room. A single squad will be stationed here half the year, and another squad the other half, on a bi-monthly basis. Drawbridges will be hooked up instead of doors, the final room will be floored completely in gold, with platinum furniture, and a highwood bed. This is mostly separate from the main fortress, which will be guarded by a battery of ballistae from one part of the map, down a 3 tile hallway, and a moat and drawbridge down the other. This part of the fortress will not connect to the caverns, but a completely separate, sealable part will be. I'll be ready for anything thrown at me, which will be mostly megabeasts I assume, as this spot has no goblins nearby. Or humans. Or elves.... *Sigh* This will be lonely.
Edit: Just remembered a dfhack script that lets me switch to arena mode and back to fortress mode. This will NOT be a lonely fortress. I'll test it out against megabeasts and such attacks, iron clad minotaurs fully armed, against my military. Each good performance will be rewarded with a beast to catch and tame, starting with bears.