Ive just come up with the concept of making the computers far more smarter.
this can be achieved through about a dozen locations and a few triggers.
for instance. seeing if you can make a group of marines follow you and then on order will move into a formation.
Cover for example.
as many locations as needed.
When ordered. cauce the marines will already be were they should be on the grid formation by following you.
then the grid will move outwards (scourges) and will leave the trail for the marine to follow. once the marine has stopped then that part of the grid will stop say he hits a wall. the grid will detect when the marine is no there under the scourge and there for he will stop.
image it as a very skillful ai system that allow for realism.