In the worst areas of France and Belgium where the artillery barrages continued for years, the farmers routinely plow their fields each spring, pick up the upturned shells and bombs, carry them to the side of the road, and the French demo experts drive around picking them up by the truckload.
Sobering work. As the shells age, they sometimes get less dangerous (certainly all rust, but seldom do they rust through!) but most get more dangerous as the explosives separate and react.
Hardly a year goes by that new construction in London, or Berlin or Dresden doesn’t turn up an unexploded bomb. I wonder why we never hear about unexploded ordinance in Japan?