Old style bombs - containing dynamite - can remain buried for decades. The potentially lethal contents
can remain dry since the bombs were dropped (failing to explode due to,say, a faulty TRIGGER mechanism - designed to ignite the bomb on IMPACT).
They are STILL therefore potentially highly dangerous. Bombs might come to the surface due to soil erosion,
farming activities, etc - and need very careful handling. The casings of a bomb might be slightly corroded -
the trigger mechanism SET OFF if the bomb is handled roughly - etcetcetra.
What applies in Germany does of course apply equally to other countries - UK, France, Poland, etc - where
'Nazi' Germany dropped 100,000s of similar bombs - and which will ocassionally come to light many, many years later.