Mulling over the earlier discussion on game-changing inventions, I was trying to think of what single item within the Dawi's current ability to produce would have the most effect. And what I came up with was the
Bouncing Betty landmine. After all, if any species is detail-oriented and obsessive enough to make use of minefields safely, it's the Dawi.
It wouldn't be much use against Skaven, between their technical ability and underground battlefields. But against greenskins? I'm genuinely having a hard time coming up with an effective countermeasure on the greenskins' part, provided the Dawi use weight triggers of "grown orc or above". You could vastly limit possible approach avenues to Karaks, have rangers plant them down in front of Waaaghs as they move - swathes of orcs gunned down without ever seeing a dwarf.
Of course, the trouble is that it would have to go through the guild approval process, but it does make me wonder what landmine-esque tech the guild already has in development.