To get rid of the rocks, edit the theme of the scenario. Most of the newer themes have the rocks removed. There are maps on which the rocks are intended to be there to restrict movement, theres not much you can do about that other than spending the time to recon your intended route before you start the mission. As far as buildings go, if you go rolling into a village in line or wedge formation, you can expect problems (especially if the town is very dense). Try going into a column formation well before entering the town. Bumping into trees and rocks etc is bad, and its pretty likely you will disable a crew member if you run into things. Tanks are pretty tough, but those soft things inside aren't so tough. Gunners dont like bashing into their gunsight.