Mine!

German forces in Italy during the Second World War made extensive use of mines and booby traps. The reading I've done indicates that Allied armies were very often forced to slow their advance to clear mines, or more unfortunately to clear roads after a mine destroyed a passing vehicle.  Some mines were designed with a ratchet system, which allowed several vehicles to pass over before detonating, so a vehicle in the middle of a convoy might be destroyed, and further undermining confidence whether an area was actually safe.

They were also notorious for setting booby-traps, as was depicted in this scene from 'The English Patient':

In Chain of Command, a defender may be allowed to deploy a minefield.  Each minefield is to be 6" square, which I understand to mean a square 6" on each side (36 sq. in.), not a measly 6 sq. in.!

Best practice for minefields is to mark them clearly, so that they can be avoided by friendly forces or civilians.  (in the modern world, leaving an unmarked minefield can even be considered a war crime, but I'm pretty certain that this convention was not in force until long after the end of WWII).  Accordingly, my first minefield is the 'polite' minefield, that clearly states what it is, where its boundaries are located, and warns against entry.

The second minefield is not so generous.  I've identified this minefield with a large crater, and the debris of an explosion, to show that someone found this minefield by surprise.  The truck is a bit dated, as it is a WWI-era Ford Model T.  No doubt either side would have been quite happy to use even a Model T to haul supplies, if they found one still running!

And to finish, here is Captain Blackadder's advice to Lt George, on what to do if one treads on a mine: