What about poisoning? Players could leave bits of food to be stolen by kobold and gnomes thieves.
If it was on contact poison, or if it somehow became injested by being splashed around the mouth that'd work. But you might want to refer more to toady's poison laced weapon traps instead for more *direct* ways of applying poison. Boobytrappingg alcohol stockpiles with gnomeblight would cause gnomes caught in the reagent to
literally melt so yeah, good application.
Or just make pots out of glass or clay, so they shatter when dropped. The greater the height of the drop, the further the contents can get scattered.
I didn't have any pre-concieved idea about breaking the barrels (making them more fragile/breakable would be nice though), in my mind like a cage trap it'd spring up and the barrel would pop out of the trap after the reagents are spilt because i dont want dwarves harming themselves after they go pick the barrel up again. It also discourages people into shoving many of them into a tight space or overlapping so that players can cover wider trap areas like a open room.
Weapon trap makes invader fall off a bridge into a chemical barrel pit where pathing back out triggers weakening reagents like GCS poison, or you have a open space unobstructed by traps covered loosely by 3x3 chem traps to slow the enemy down travelling the 'easy route' around your traps.
If a metal barrel is full of lava, the barrel & the trap mechanism would need to be lava proof once it is cleared to be reset, same goes for anything with other sensitivities but thats a extreme application given how last resort a lava trap may be.
- Players would undoubtedly find ways to creatively use barrel traps, such as dousing gremlins & FB in dizzyness inducing cave spider poison so they bypass [TRAP_AVOID] once they injest it or come into contact with it. A FB silk farm providing you have a correct type (doesn't fly, no other negative features beside webber) may be possible if you drug the FB with a barrel trap first before trapping.