That war server sounds like a whole lot of fun, and if there's a Bay12 nation everything is set for dwarfy fun! I've gotta check thier site to read more and see if they accept more people anytime soon.
Oh, and yeah, the regennerating house linked earlier was nice, but then the guy made this:
http://www.youtube.com/watch?v=4p2Gga6dIWY Put the redstone and trigger inside the walls with a centeral keep and you have instant castle walls that have the added bonus of self-repair.
"INVADERS! LOCK DOWN THE CASTLE! THIS IS NOT A DRILL, PICK, OR SHOVEL!!!!!"
Evrywhere blast doors are closing and guard posts/traps are readying as everyone scurries to thier posts to avoid getting locked out, burned, shot, stabbed, drowned, crushed, blown up or RDSed (Rapid Decelleration Syndromed) by the defence systems. Dispenser batteries! Mob launchers! Scatterbombs! Lava curtains! Corridor floods! The Skelle-dungeon to Courtyard minecart express (You can pick up mobs in carts, right? Sounds like they would make good turrets.)
I wonder if they have any interesting mods on that... Telsaing and nuking from IC, as well as HV used for triggerable deadly floor stripes... Buildcraft automaticly resupplying dispensers with arrows from the mob farm... Oh wait, this is a server that bans automated mob farming, or even low-risk. Well, We are just gonna have to make it even more insanely deadly, make a back door through the dungeon, and call it a "Loot-recovering PC trap" that feeds into the main sorter that just happens to massively stockpile products of the mobs.
EDIT: Hmm... Looks like very little for engineers to do. "Redstone is for doors" and all that. "No non-melee drops" (I think player-launched arrows also work)... No high-tech mods is understandable, but why not let us use the tools we've got? As it is, you could "Get hit by lightning" for accidently leaving an overhang to close to a decorative cactus! Grows too high->block drops -> somone picks it up -> it is an honorary "mob farm"... I understand not wanting it be "first to build a spawn tower wins", but still, it looks like even a stock minecraft door is against the rules (allows one-way melee). Im sure they wouldn't take the silliness that far, but where do external fortifications and defences end and nighttime farms begin? Any particularly ingenious trap or dark labyrenth could be squeltched by an admin with the words "mob-farm!".
I would rather just have it so redstone and such is concidered precious and therefore "pillagable" in war...
Looks like, even if I COULD get in, I'd have to <gulp> trust the admins.
EDIT 2: Oooooh, they let current members refer still...