Blamelesscloister has survived thirty years, sitting on a glacier bordering on a taiga. The first year was characterised by defence against yetis, after that it settled down to animalpeople from the taiga. We _could_ grow surface crops if we bothered. All living quarters and most workshops are built into the glacier, with many workshops built from ice. Rooms in general are quite lavish, the ducal suite takes up a few hundred tiles; well, you have to spend all those years _somehow_, and mining and engraving aren't the worst uses of time and ressources. There's a magma workshop with two forges, two smelters, a glass furnace and a kiln in the topmost stone layer (carted magma up over a hundred levels from the magma sea, not-automated, so each workshop has a measly one-tile 4/7 pool under it).
With several dolomite layers containing rich lignite veins and massive iron imports from three civs (dwarf, human and goblin), the five militarydwarfs are clad in finest steel and weapon traps are also equipped with that metal.
Population cap was set low enough to ensure no migration past the first year, the fort has grown to its current 86 beards entirely by natural growth. Fourteen dwarven lives have been lost on the site, as many as elves died here - mostly from goblin ambushes, although a handful fell victim to a pathing misunderstanding.
Considering the very poor results they have to show, the goblins have been remarkably persistent. Just over 550 hostile units have not returned from the site, 475 of them were killed and 84 captured.
Most dwarven losses were suffered in the earlier years, when the main defence strategy consisted of cage trap spam around a single entry. It took me a while to learn that cage traps as goblin defence make most sense as _second_ line, to catch stragglers that made it through weapon traps. Furthermore, ambushes' invisibility strongly suggests a defence design that's not just based on "inside" vs. "outside", but rather sets up perimeters - an "outer" range that stands undefended, a "near" range, where the active defences like traps are stationed and a "core" area with some passive measures like security doors, stationed warbeasts etc. but where hostiles should never reach; and all of them must be strictly separate, so that you can let goblins into the "near" kill-zone, let the traps do their thing and lock that area against the outside, so the haulers and mechanics can clear the zone without getting molested.
I eventually constructed a minecart grinder and dedicated my further work on this fort on observing and if necessary refining this defensive measure. There was very little adjustment required - use raising bridges to open/interdict path into the grinder so you can keep traders and diplomats alive, load up the carts to have sufficient weight to shift war beasts - the core design is pretty intuitive and worked very satisfactorily right out of the box. The grinder has accounted for 210 out of the fort's kills, and the vast majority of kills which occurred during its activity. As with other fully-automated traps, the main problem is not getting it to kill things, but rather to kill the _right_ things. An "enemy vs. friendly" filter promises to be a decent challenge, esp. since i'm playing unmodded and thus have many microdwarfs who don't trigger pressure plates; and friendlies (caravans and diplomats) are 100% trapavoid, so giving them a path that a trapavoiding hostile _won't_ take seems difficult.
An alternative "on demand" minecart cannon, launching carts when a pressure plate gets activated, was not nearly so effective but fulfilled its intended purpose which was to soften up sneak squads on their way to the weapon and cage traps. The installation even scored a few kills - lead minecarts propelled by highest-speed rollers can put a bit of a dent into a goblin.