I am afraid that won't work here. This is going to be a three way fight. The player is resistance - friendly to nobody. I want the east and west guard units to go after Resistance at all times in the game, but I don't want east or west to go after each other until much later. East and West convoys alternately visit the check-point (it is really a trading post) so I can't have resistance units there either.
I think I will just have to make sure I don't have east and west at the check-point at the same time. A pity, it looked really good.