Visibility priority

Is there any possibility to create visibility modifiers with higher "priority" than unit vision?
What I'm trying to do is to define a region only one player cannot see, even if his units stand right next to it. I can't use sightblockers, since any players can see them (and can't see through ).

thx anyway

I think this can't be done, unless you can make certain sacrifices. For example, a possible solution would be to have a bunch of invisible unselectable flying units following every unit except the units belonging to this certain player. Then vision blockers should do the trick, other players would see over them thanks to their flying followers but this one player couldn't. Of course, in this case the other players would see over all sight blockers and could also see across cliffs, and this one player shouldn't be able to obtain any flying units. You can fix the first problem by dynamicaly adding and removing flying followers so only units near the one-player-vision-barrier are given one, but there's no way to fix the other, with such a solution the one player can't have flying units.

Why not give the units in question no sight range and then give a ground unit (with no pathing) that follows, a sight range. That way cliffs and all that still block the sight, and the player who doesn't have a unit won't be able to see.

Note: If a player cannot see where a unit is, the player will not be bale to select them, even if the unit belongs in a numbered group ( ctrl + # ).

Oh well I'm sorry I didn't make this very clear :
I want a unit (only one controlable unit per player) to not be able to see what's behind it's back. I had a trigger create a visibility modifier behind that unit every 0.01 seconds and it seemed to work at first. After some minutes however the units circle of vision breaks through ("overwriting" my modfiers for several seconds).
Ahw I really can't explain it ^^'. I just need to know if there is any way to fix this or if I have to search for other solutions (I'm doing that anyway though ).

Thx to Ammorth and Anitarf but I fear that won't do the trick.