That sounds less than optimal.
I have a better way (I even tested it out!). I added ruleset.mercGONE to the Definition file, and put it in with mercON and mercOFF in the context tab. Then I added '!ruleset.mercGONE' to the Member Tag Expression on the individual units.
I'll send you the files, Butcher (check your PMs), I made all the necessary mods to my files. I love it when I figure something out!