My newest fortress WhiteCastle(Mk II)'s serrated disk traps were showing to be far more effective than I planned. And I figured out why.
My fortresses usually have a single line of serrated disk traps, with one disk in each. It's more intended to soften up attackers for my military than to repel attackers by themselves. But so far those alone have been repelling ambush attackers for 2 years.
My fortress is built next to a waterfall, and I have the moat feeding from the upper river and draining as a second waterfall into the lower river. Due to the moat being too close to the waterfall the water is only about 4 deep at all times. And the serrated disks are adjacent to the moat. That ended up being important.
Recently I discovered a large number of goblin and orc corpses at the bottom of the manmade waterfall at the end of the moat. All in full combat gear. After a short time puzzling it out I discover what is happening.
The ambushers are crossing the moat to get attacked by the disks. The skilled goblinoid military is dodging the traps without much difficulty, as expected. But they are dodging INTO THE MOAT, there the unstable 4/7 water flushes them off of the end of the moat and 5 z-levels to their deaths at the bottom of the waterfall.
I have unintentionally created an automated mega-deathtrap. I feel all warm and fuzzy now.