We attended a metal detecting safety course.
Digging in the ground looking for metal, in Germany, it's possible to encounter unexploded war time devices. Unfortunately, last year a backhoe operator hit and exploded a WWII bomb. The tremendous blast killed him and broke windows miles away. Fortunately, most unexploded munitions require much force to detonate. My son and husband have been metal detecting for over a year and have found lots of bullets, aluminum foil, bottle tops and a few coins. If bombs are discovered, it's best to leave them alone, place a marker at the location and call the guys in the photo below, or just call the police.