As the title says, I'm looking for thoughts on how to keep my civilians out of ambushes/sieges/etc.
Before I continue, yes, yes, I know burrows are "the" answer - but I have this sprawling underground fort, constantly expanding, I really don't want to paint the entire thing a burrow and have to add every single level of each mining shaft, ever Armok-blessed vein I dig out, onto the burrow.
I only have this one surface exit, covered in traps, with a lovely magma-flooding-and-draining system, and just past it is the barracks with a pretty decent military if all else fails. I want to leave it open, and funnel all sieges and caravans and whatever else through it, I just need some way to keep my civilians out of that one entrance without needing to paint the entire underground expanse a burrow.
I've manually mass forbid everything aboveground, I have no hunters/fishers/woodcutters/herbalists/etc, I've done everything I can with the 'o'rders menu to persuade my dwarves not to collect enemy or friendly corpses or any item they drop, not to mention any refuse outside. Anytime someone/thing manages to die outside, I manually mass forbid it too. I even have indoor water sources. Yet somehow my treehugging elf-sympathizing beardless civilians find some reason to wander around outside, usually to "store item in stockpile" - even though, as I've said, I've forbid everything on the surface. I never do find out what any of them are after, since they don't live to get far from the fortress. Although sometimes they just wander out there with "no job" or "on break" just for the fun of it.
Is there a way to "forbid" that one entrance somehow, we're talking about a single tile here I need to keep civilians out of, while still allowing sieges/ambushes/caravans/new migrants to pass through? Without painting who knows how many z-levels of underground as part of a massive burrow, and painting more every time I dig a little deeper?
Edit: I've also tried forbidding a door, but that seems about as bad as raising a drawbridge - it keeps invaders and caravans and migrants out as well as keeping my own dwarves in.