> It would be such a little thing to dump the earth they excavated when building the bunker back on top of the thing and spread it around so grass grew etc, hiding the damn thing.
Easier said than done, and I don't think camouflaging them was ever a priority. Even today, you can see the excavated material spilling down the hill in front of large bunkers 70+ years later, which makes them fairly easy to locate: https://www.cios.org.je/assets/images/other/noirmont-headlan... (this location is also easy to spot in wartime RAF reconnaissance images that I've seen)
Easier said than done, and I don't think camouflaging them was ever a priority. Even today, you can see the excavated material spilling down the hill in front of large bunkers 70+ years later, which makes them fairly easy to locate: https://www.cios.org.je/assets/images/other/noirmont-headlan... (this location is also easy to spot in wartime RAF reconnaissance images that I've seen)