Basically, what you want is a unit to stand on one place. Some units like the marine can attack while disabled, I think (correct me if I'm wrong on this one). How many units like this will be placed?
If there will be a lot of units like this, I have only one idea:
When a unit like this is created, you create a burrowd computer unit under him. If you do like this, there wil lbe a burrowed unit for each "fighter unit", and the burrowed units will represent the spot where the fighter units were placed initially. Since you have two computer slots, you must center a 1x1 (pixel) location on them (the burrowed units) one by one (see "grid" in the tutorials if you don't understand what I mean). If you bring exactly zero units of the needed (fighter) type in that location, you must get the closest unit of that type back in there. To do that, you must have another location that's the size of a turret (since you can't build a turret closer to a unit than the turret's own size, and let's hope the unit won't leave this location by the time the trigger gets to it) and center this location where the 1x1 pixel location is at, and move 1 unit from location A to location A (A is the turret size location). If you have zero units of the needed type in location A after the "get unit back" trigger runs, this means that the unit is dead, and you remove the burrowed unit at that location.
The tricky part is that the unit can leave the turret-size location when you have a lot of units placed like that, so you might want to use different types of burrowed units to run multiple cycles (like described above) at the same time. And also don't forget - if there are too many ground enemy units around your unit, you can't move him back.
If you have only a fiew units, that must not move, you can simply center a 1x1 pixel location on each, and the rest is easy...
OK, I may be bad at explaining, but that idea should work fine...