In the real world, they often make firebreaks to defend against fire: a strip that’s cleared of everything flammable, whether it’s buildings, trees, or whatever.
In realms being invaded by the city of Dis, and whether other supernatural threats loom, they make felbreaks. A felbreak is a strip of land (or sea) cleared of everything known to provide nourishment to demonic, eldritch, and otherwise preternatural invaders: people and creatures to sacrifice, empowering relics and magical artifacts, etc. Felfighters remove curses, lay ghosts to rest, and encourage people to not perform divinations in or for the felbreak.
Sometimes it works! A DW front involving an advancing unnatural threat can be stymied by a successful felbreak, pushed aside like a classic vampire held at bay by the upheld cross or ward of a true-believing vampire hunter. The threat may turn, or retreat, or dissolve.
Sometimes it doesn’t work. Fire can leap across too-narrow or insufficiently-thorough firebreaks. Unnatural forces can stream over, under, or through a weak felbreak. Then it’s the defenders’ turn to fall back.