Just had an idea, only semi useful but wondering if anyone else has tried it.
Set up a working Pipe system above each zlevel of "rooms" being pumped from a Self Powered Pump.
Now instead of building a normal "Doorway" build the door way so its 2x1 like so
######
#OOOOO
#OOO##
######
Put the door as marked;
######
#OOODO
#OOO##
######
Then on the open space infront of it build a "waterfall" that falls into a grate and thus the "piping" for the layer underneath.
#######
~~~~~##
####~##
OOOD~OO
####GG#
What does doing all this acheive?
In the event of a siege or even something as mundane as "Cleaning" you can flood your fort (after setting off the alarms ofc to get everyone in a room nearby.) with Magma.
What this will do is Obsidianise each doorway thus making it 100% safe from pretty much everything even destroyers (its not constructed see ^^).
For safety reasons I whole heartedly advise each "Saviour Room" contains as a minimum the following 1xLever which turns off the magma flow, 1x pick (to get out ofc), 5x5 Stockpile of food and a 5x5 stockpile of boozer or 1x well.
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If that isnt hard enough: variation:
Change it so that instead of doorways it does this to corridors. In turn you can even set it up so that each "Corridor Waterfall" can be turned on and off by use of hatches meaning you can manually divert the flow of magma to anywhere in your fort without too heavily affecting service else where. (assuming labour is compartmentalised, farms near stills n kitchens etc.
Naturally I dont need to say... magma safe, and a dedicated lever worker needed.