Let me give you an idea of what you are up against when trying to attack a town. I have been playing for many years, and one of the things that I like to do a lot is Ant Trail Interdiction. I can usually spawn into a town, take a look around and judge where your FRU is most likely to be and what route you will be taking to get into town.
Now don`t forget your new marking method will go both ways. Since I already have a good idea where you will be showing up and I can mark and track you, you will not get any closer to town.
On a side note, weed and tree lines show up as slight discolorations on your map if zoomed in all the way. If you spot something you want to mark, say, the next weed line over from your position, just zoom the map in as far as it will go and make your mark on the next discolored line on the map. It will be almost spot on.