you are incorrect, and dealing false information wd40.
I tested this out (with no triggers) and the units walked fine, till they ran into my line of towers and "stopped".
Problem is, they dont stop, per say, they are still being issued the order to move and will continue to try moving towards the location, or as close as possible. Until an obstacle is removed, they will remain there but they arent stopped, thus they dont attack. I already check and yes the enemies can attack my towers (when they are stopped) and they ARE enemies in the game.
I still need a trigger for this...