Ok … but if unit which reached the target activates 1 more obstacle, which will “close it” in a box, this target will be unavaliable, and next units will behave like I’ve described, Am I wrong?
EDIT: If this doesn’t work, would you like to tell me where should I attach your script (Which options of the asset are best for RTS (like Starcraft II)) to get wanted effect? Or is there somewhere a scene where I can look and see how it works? 
EDIT2, AFTER ARON’s post below (I can’t add anything more because I’m “new user”)
So long hours of testing before me 
Of course, my idea showed with my paint images wouldn’t be the only one, it’s more like “for security”. Perhaps I’ll try to do something like in first “Sudden Strike” games: Selected Object from the sorted list (with 0 index) gets original targets. Then there’s a calculation for destination between object [0] and next object. If this distance is big, it’s multiplied by some kind of factor (bigger distance, lower factor), and a new target for next object is calculated.
Sorry if I discuss too much, but I’m still learning and I hope our discussion will be helpful for the others someday