Here's my current, and probably most successful, fort. Archers are set on a patrol of the fortifications, with the moat guaranteeing that they are within shooting range (my math might be a little off there but it should at least prevent most enemies from hanging out under their sight range.) The moat is dwarf-made of course, and the bottom section of the river was channeled to allow the moat to flow more reliably. The top part of it is the original brook, simply channeled out to prevent enemies from walking on it.
The aboveground section is sealable with drawbridges, and there is a more complex staging area underground with cage/weapon traps and an emergency drawbridge seal. The plan is to move those traps aboveground in front of the drawbridges and make the aboveground fort the complete staging area.
I've been terribly unlucky with iron and flux for a long time, and this fort was no different, but this time I was resolved to focus on what matters: Candy. I dug down to the magma sea as quickly as possible to offset the complete lack of advanced metals (not even tin to make bronze!) After striking a candy funnel without 15+ z-levels of no hollow section, I was partially set, my weaponsmith was high enough to make quality weapons.
Soon enough I've got 16 soldiers, 8 of them with adamantine weapons and the rest with silver warhammers and copper crossbows. Copper armor does the job for the first few invasions since adamantine is so labor intensive, and more importantly i'm able to buy/loot steel for melting purposes to get my army up to a respectable standard. We're only 5 years in, so the kill count isn't overwhelming or impressive.... but we've got 3 goblin ambushes (one with an elf civ member!) an ettin, and three werebeasts under our belt. Not to mention the one-eyed web-slinging rat titan that managed to break two unlucky necks before going down.
Nothing too fancy, just proud of myself for not messing up. This is the..... 5th? fort in a row where i've tried to do this over the last month, but each has failed before the actual structure stage. The first was lost to a werebeast attack, since I goofed on getting military up early. The second to a werebeast infection that I failed to contain within the allotted month. The third to a necromancer raid who showed up with 70 soldiers well before i had 70 dwarves........ And the fourth to a terrible flooding accident as I goofed up my usual generator/bathhouse wombo combo design.