Walls are nice, but if you make a large, thin scaffolding as high up as you want the wall, and place lava on the scaffolding, and then build a wall around the lava, you've got a 5 block thick wall with lava as the inner 3 layers, plus, the 3 block wide surface area at the top would be good for external defense,a dn the lava would greatly discourage people from digging through without a few fireproofing potions, which are hard to come by.
If they can and want to dig through the walls, they'll just plug the lava holes as they go. It's not a terrible idea, but there's probably not much practical gain beyond a normal 1-block wall.
if we have the resources, iron golems at the entranceway would do well, if we contain them in fences, and snowgolems, although they are weak, make good distraction, and their snowballs still damage armor.
We don't even know if these are going to exist. If they did and it mattered, I imagine we'd just pack the walls with snow golems anyway. I'm unfamiliar with the exact ratios, but unconvinced iron golems would be more effective than dwarves wearing and wielding said iron instead.
at the wall corners, guard towers made of netherbrick fence would look nice if our god was earth or fire, as they would fit the theme. on the wall perimeter at the top, we stagger fortifications, with dispensers filled with buckets of lava inside, and levers attached, so that anyone who tries to climb the wall gets a nice dosage of hot magma on them. if resources permit, and obsidian farming is allowed, we make the wall 7 blocks thick instead of the 5, with stone or nether brick being the external, and an all obsidian layer below that, with the lava sandwiched nicely between that.
More fairly useless pile-it-on planning. We're not going to have enough obsidian to build a respectable wall out of, and even if we did it probably wouldn't be worth it. Also note that encasing obsidian in other, weaker materials just gives them a ready-made shelter to hide in while they work on it. Even if it was more useful, I doubt we'd have enough arrows to make delaying tactics like that worth it. The dispensers would be unlikely to catch any targets, magma being slow and predictable and all, and almost assuredly wouldn't have any function over just giving the button-presser a lava bucket or two.
the buildings inside the walls should arch around the center in a conical pattern, to give the longest possible pathway from the center to the main entrance, in order to give us additional time to prepare adequately.
Forcing a long run is going to be almost completely worthless as a delaying tactic, which is already worthless as is. There just isn't enough space to buy any reasonable amount of time for the effort, and if there is, it'd probably hurt our respawning and rejoining the battle efforts more than the enemy's gutting of our central whatever it is.
there should, of course be a moat around the fortress, and I propose that there be a drawbridge made of pistons, so that a person on the other side just has to flip a switch to give people access to the other side. of course, people could always simply climb over it, so our archers should be adequately prepared.
If you have plans for a lengthy and completely retractable drawbridge feel free to share them. A moat could be mildly useful, since water genuinely slows people down until they can get to a place where they can build again, but again I don't think we'll have enough arrows for it to matter all that much.
in order for our fortress to prosper and be protected to the best of our ability, we would need a few specialized jobs, besides miner, warrior, etc. we'd need obsidian harvesters, gravel diggers, alchemists, artificers, dedicated smelters, and dedicated mob hunters who hunt with their bare hands to conserve resources. if all of these things are possible, and we have a large supply of everything we need, our fortress would be nigh unbreakable, save massive zerg rush, but I doubt that would ever happen.
Voluntary Minecraft labor does not reward specialization in any manner beyond presumably better coordination. Thus, having dedicated jobs on that level is beyond worthless and should never be suggested without a very good reason. I can also fathom no shortage of wood or cobblestone that could possibly justify completely unarmed mob hunting. Calling anything unbreakable in Minecraft is roughly on par with calling a ship unsinkable.
of course, since a good dwarf needs to be prepared for everything, I propose that we add a doomsday device to the fort attached to the lava systems surrounding it, to prepare for a worst case scenario. at the height limit, we add thousands of of dispensers filled with lava right above it, and if our strength ever becomes broken, we pull the lever. no regrets.around the moat, to ensure that people don't dig under it, we need to make the moat really deep,so people don't get any ideas. how's that for on-topic defennse?
We are not building an enormous, ugly-as-sin contraption way up in the sky and as large as the entirety of our base (which might not even be mostly aboveground anyway) just so we can cover everything in magma as a doomsday joke.