Disenchant, Mana Leak, Force of Will, and some other cards can stop it...
Muscle Sliver can cancel its effect. I think those were also some of the cards used in Countersliver too...
But I'm just being bitter. I would SO play Countersliver, but I'm lacking the mana base for it. I have pretty much everything else (heh, I have four each of every Tempest/Stronghold sliver), but that's not enough...