Here is an idea. How about drawing a supply line on the terrain just like you would draw out a set of walls, except in this case the "towers" are supply depots and the "walls" are dotted lines (that show up when you select a depot). The lines would be much longer than the longest wall, of course. You would drag these from your Civic Centre out into the map into neutral and enemy territory. Units within vision range of a depot does not suffer attrition or each depot has a supply aura. You can disrupt an enemy supply line by destroying a depot along the way. Supply lines would cost Food, simulating that the most important supply of all is Food and water. Anyway, not saying we should add this, but it's an idea nonetheless.