Improvised explosives Carl built to detonate only for hunters, to be placed sparingly along the roads.
Carl has multiple IEDs built and designed to be triggered only by Hunters, and knows he needs to be careful with their placement so as not to waste them. Placement is complicated by what Miriam Dom told him: the main caravan road south is mostly clear of traps because caravan bodyguards cast anti-trap spells as they travel, and those spells disarm even traps built specifically for crawlers.
Carl passed the intelligence to Katia and asked her to spread the word so the regular caravan routes could be added to the Community Map — knowledge that governs where his devices will survive long enough to matter.
Improvised explosive devices of Carl's own manufacture, keyed to detonate only for hunters.
Carl's scarce, selectively triggered road weaponry against the incoming hunt.