Berlin did a systematic search up to the mid 70s, at this time it was assumed that all the EOD would be safe due to detoration. This attitude was quickly changed after a 500 kg bomb with a delay fuze exploded without a warning under a street in Buckow in, I think 1978, fortunately nobody was injured, since it happened early on a morning on a weekend, when most people were still asleep. Shortly afterwards it was discovered that a whole development has been built over a former anti tank trench, which was used in the month after the German surrender to get rid of ammo, including hundreds of Riegelminen.
This caused a big stir, since houses had to be evacuated for long periods to permit the authorities to recover the ammo.
Systematic search was taken up again. Another push came after unification.
Some builders, who were drilling holes for foundations of a new building in Berlin-Lichtenberg (standard practice in Berlin. The cities underground is sand, gravel and clay, with the bedrock almost 800 meters below. To get a stable foundation for a building, rows of holes with a diameter of about one meter and a depth of 20 meters are being drilled into the ground, and then filled with a reinforcement cage and concrete). In this case the drill bit hit (as has been reconstructed from fragments) the fuze of a dud 250 kg bomb, killing three builders, injuring several others and badly damaging several neighbouring buildings.
At the same time the British and Americans declassified their after bomb raids areal pictures, which permitted a better search.
The project I was working in (in a very menial position, as a summer job wielding the shovel as a college student), was a systematic search of the Tiergarten park in West Berlin. Every day we would mark an area of ten meters times 50 meters and divide it in lanes of 2 meters. The search was done using both mine detectors for any metal close to the surface and Förster probes to search for ferrous metals down to 3 meters. Any piece of metal had to be accounted for and had to be entered into a map.
EOD search is a state matter in Germany, as you know, so laws vary. In Berlin at least the grounds of every new building project get searched. Unfortunately there are many areas, where houses and factories have been built on land not cleared in the past. They may be standing right on top of unexploded bombs.
Jan