*Well actually*.
I'm pretty sure it'd be possible to have, on certain maps, fortifications which you can place snipers/infantry behind and have them fire over/through holes, and have varying levels (concrete > impervious to infantry fire, weakish to tanks, taken out with artillery; light fortifications > takes some infantry fire, anything bigger wrecks it), so that the enemy firing upon it *could* get through the firing zones but their inaccuracy at range would come into play, OR the model could possibly be made so that it is a 1 way system.
Then we could have either ruins or forts which aren't annoyingly linear bunkers.