another question:
There are several units placed in a location. I've ordered them to attack any enemy unit that comes into that location, and when the enemy is out of that location, they should return (move or patrol) to the location. But now they al go back to the center of the location. How do you set them back to their previous position instead? (without making locations for every single unit).

Often computers will do that on their own... Other than that there is really no way, unless you wanna run through all the units, place a burrowed unit under them, then order them..

I cloaked some buildings so they were not visible when any player unit approaches.
when the unit leaves that area and the area becomes dark again, all normal buildings are still displayed in the fog, as should be. But the cloaked buildings are now visible as well! Is it supposed to be like that?

THIS IS STARCRAFT !
yup, it is normal for every building to appear in fog, even if they are cloaked...
and there is nothing you can do except giving vision over the area with map recleaers or other units.

no, I meant cloaked buildings should not be visible, so not visible in the fog as well. I'd like the cloaked units to be hidden as much as possible, and not to be revealed this way.

Yeah... Nothing you can do about that, it was always funny in Team Melee games to cloak Zerg buildings, then if the enemy wipes out your base, they go searching for it, then notice they missed a building, come back, find nothing, then go to leave again and see it show up again