From the headline I thought it was going to be about the variously shaped concrete blocks, e.g. Dragon's Teeth [0], used as anti-tank defences, which can still be seen all over the British coastline[1].

[0] https://en.wikipedia.org/wiki/Dragon%27s_teeth_(fortificatio...

[1] https://citizan.org.uk/blog/2017/May/31/humble-anti-tank-blo... & http://www.pillbox-study-group.org.uk/other-wwii-defensive-s...