Berms

John the Gingerbeer espoused:

It was pretty conclusively demonstrated in Desert
Storm that bulldozed berms of sand are pretty useless.
 But a proper tank fighting position is something else
entirely.

[Tomb] Given. But here's another point: Normal armour for tanks is in 
the area of armour 3-5 (3d12-5d12). Adding a D6 ain't much. Perhaps 
the discussion should be: How big of a round will be stopped by a 
prepared tank fighting position (possibly concrete included)? By a 
quickly bulldozed sand or dirt berm? By a rocky outcrop or ridgeline?
I'm guessing the sand berms might not stop 120mm rounds, but might 
stop (just throwing some out) low-velocity 73mm guns, ATGMs, and 20mm 
cannon. Thoughts?

Additionally, the ground type may play into it - I'm thinking being 
behind a good ridgeline in Ontario on the Canadian Shield is like 
being behind a couple of inches of dirt then solid granite! That'll 
stop or deflect a pretty big round. And out West, if you get Prairie 
hardpan, it'll be almost impossible to entrench without vehicles or 
explosives, but it would deflect (once you had entrenched) far better 
than typical temperate climate earth.