I would resort to triggers that look for a footprint between the target and the attacker.
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Considered easy altering of the unit textures?
http://static.sc2mapster.com/content/attachments/15/252/Screenshot2011-04-17_09_16_21.jpg
For my public assets look here!
http://www.sc2mapster.com/forums/resources/data-assets/46733-the-assets-of-evil/#1

Project_06 Regular ShmoeYea i suppose, this problem is really making me question continuing with the map, because this could cause major problems as i progress through making the map(it wouldnt be a problem if each player owned a single unit but that is not the case).