I made dragon's teeth for the Bulge scenarios, so they can represent antitank ditches I suppose. The maps are made up of thousands of 100m grids. Only rivers (line entity) and major river/lakes (area entity) can ensure that movement is completely "wiped out" along the entity. For example, a unit can cross a stream or railroad without any penalty as several (invisible) locations. I had to make the dragons teeth graphic wide enough to ensure that movement across them was completely blocked. This is a pain to do, because you constantly have to compile the map and use the wheeled movement tool to check that wheeled units cant cross the graphic.