There is also this flag too: <PreventStackingWith>spell name</PreventStackingWith>

so you choose what you want to stack with or not.

Ah, thanks.

But as far as unit abilities go, if I give an ability of say, +1 Army cutting attack to a unit via unit ability, is there and anti-stack for that?  I tried CanStack, but it didn't seem to work.  But maybe I misplaced it -- anyone ever get CanStack to work with an ability like that?  Meaning I would like to make the benefit non-stackable -- only one per army.

Sorry, I thought we were talking about abilities as in spells. Yes, armywide abilitybonuses always stack