Juggling your invaders.

You have two entrances, each with the typical maze of traps. During an invasion, you close one entrance and leave the other open. When enemies successfully get through your gauntlet, close the door and open the other, forcing them to go over your trap maze again to get out. Juggle them between each entrance until the invasion is over.

I just hope your lever pulling dwarves are reliable...

Build magma mines (I guess they become lava by then). Always wanted to do that, have never had the patience to do so.

I wish I was less of a Dwarf Fortess poser. I love it so much, but I always find it difficult to sit down and play.