I tried pumping out the water from the canal on my previous turn to get someone build a grate there, and it ended up drowning a baby. I'm not sure if I want to mess with magma too much.
I've played a bit, but the FPS is horrible. It's going to take a while. Btw, what was the idea of the cavern airlock-thing? We had a little showdown where the FB corpse was hanging around. Now we have two of them. Luckily, the other one seems to stay dead.
The idea was:
1. Build big room with lots of spikes [check!]
1A. Station strategic dog, duck and kitten reserve in place [did some of this!]
2. Wait for the FBs/undead to move away [...not check. They moved closer instead]
3. Send brave miner to dig through into cavern.
4. Close bridges behind miner and in front of undead FBs before they rip said miner to pieces [this is hard]
5. Use strategic dog and kitten reserve to lure in undead while keeping the inner bridges closed.
6. Put spike lever on repeat and go and have lunch or whatever.
(All levers are noted, so you can see what they all do. They're on the same Z-level as the room itself. The mechanisms for the bridges are fairly low quality, so they take a while to actuate)
Whether it'd work or not....dunno. Really, I didn't use enough spikes and made the room too big. But if things move away from the would-be cavern entrance......it might be worth completing it and trying it out. Just don't let things actually get into the fort. Those undead are nasty.
Edit: Oh. And the way the caverns undead are working: If something dies
under the lake it will come back as a zombie sooner or later. If it dies under the land, it's not in an evil biome, so it won't rise from the dead (this is why the airlock is actually viable in theory...rekilling things in there should stop them reanimating).