Perhaps a "Nullify X" bonus? X would be something such as "attack", "damage", or "power", and the Nullify ability would read: "Any changes to [whichever stat is affected] during the round that [the card or, in this case, clan] is played have no effect.
Leader abilities are unaffected."
I understand it's kind of an upgrade of "Protection: X" as it would stop + effects, too, but I look at it like this: Best case scenario, it's an All Stop vs. double modification of the same thing (plus an ability/bonus--rather strong, to be sure); worst case scenario, it has no effect at all, like an SoA against Lohvak,
Tyd, etc. It would, however, prevent that clan or card from changing the statistic, so it doesn't seem to be broken IMO. Thoughts?