I recently got lucky enough to get one of those lovely upright adamanatine weapons in an embark, so I saved a backup of the fort and am trying different things with it. Of course first I had to release them just to see what happened... and wow, they weren't kidding when they said it was FUN. Mass slaughter, even with a military that included at least a dozen legendary dwarves, and nearly fifty total, none of which are raw recruits. (Goblins in cage traps, plus arena and live-target archery range... Trained them all up with maybe twenty total military casualties over the life of the fort. Very nice.)
The way I'm experimenting with now is multiple bridges, enclosed--break up the stream of clowns into small, manageable groups--use fortifications to shoot bolts at them, soften them up. Won't necessarily fall to the bolts, or to spike traps; so you have to find ways to clean up the ones that don't fall to piercing damage. I'm thinking steel-battleaxe dwarves...
The syndromes are giving me the most trouble with my design. I'm considering routing some water through there to clean off the bridge area periodically, and isolating the area itself with a dwarf-washer to prevent syndrome sludge from getting tracked into the fort proper.
Going to have to figure out a way to deal with the inevitable unhappiness from dwarven deaths too. Those aren't preventable because of deadly-dust attacks and other ranged attacks that can go straight through fortifications. So... I'm thinking a kitten drop in the dining room? But I've never really had any success with getting them not to care about anything by just dropping kittens. And if I drop children, it's risking a tantrum spiral.
You could just do a dwarven checkerboard, but that's a bit cheaty. And anyway, your dwarves don't actually get to kill the clowns themselves that way.
It's essentially a matter of fighting endless Forgotten Beasts, all of which can fly and all of which will go straight to your dwarves and start slaughtering. Rather interesting strategic challenge.