Is there any chance of the addition of an unbuildable (though invisible and passable) overlay for the next version of DTA? Assuming it's possible, it would greatly help mappers control the AI (for example, placing it on bridges to prevent locks, stop them from building up cliffs impassable to ground units, or making certain terrain features passable but unbuildable (such small rocks and those wall-looking road tiles), some of the most common and irreparable problems in the maps ).