Booby-traps were devised with delayed-action fuzes used a striker on a spring, held back by a wire. Acid ate through the wire, to release the striker and detonate the explosive. A number of devices with such fuzes were planted in bunkers but most booby-traps had simple pressure detonators. Wires were attached to useful items like stove chimneys and loot; trip-wires on the stairs of dugouts were connected to bundles of hand-grenades. On some roads, heavy-artillery shells were buried with contact-fuzes, which would only be triggered by the weight of a lorry. British engineers and tunnelling companies scoured areas as they were occupied and disabled many of the explosives. Roads were flooded by destroying drains and water-courses; wells sabotaged by drilling a shaft next to them and exploding a charge, permanently ruining the well. Much of the explosive used by the Germans (, and ) had the property of water-absorption so could be neutralised by dousing. Some British booby-trap patrols made German prisoners go first, who revealed traps rather than be blown up and British tunnellers removed of explosives. (In some areas no booby-traps were found, as German divisional commanders had been allowed to choose whether to mine their areas and some refused.)