if i understood correctly that you want a unit not to be able to move, but still to be able to turn towards combat, here is a solution i used once:
1) make a buff based on whatever
icon = your unit icon or whatever
art --> remove all effect models
tooltip = whatever
2) make an ability based on ensnare:
mana cost = 0; casting range = 50;
duration = 0 //means forever (if that is what you want)
buff = our buff from above;
targets = ground
3) do this whenever a unit is created and revived (or becomes static)
Unit - Add SelfEnsnare ability to OurUnit
Unit - Order OurUnit to Orc Raider - Ensnare OurUnit
Unit - Remove SelfEnsnare ability from OurUnit
4) that's it; if the unit can become mobile again, there is a trigger action called: Unit - Remove specific buff...
hope that helps