I was thinking about this while in bed this morning. So we know that for some reason Smokey can't move through a circle of ash, and so far the ash we've seen has been black (volcanic ash?).
But Ilana is holding a bag full of Jacob's ashes, is it possible that Smokey will be vulnerable to these, or they will offer some sort of extra protection?
As an aside I think half of this popped up in a dream and it meandered to where I had another thought (although I'm this is mostly just spitballing) - that the ash we've seen around the cabin and the temple has been black, perhaps relating to MIB somehow? And Jacob's ashes (as far as I remember, I could be mistaken) were white, possibly indicating that that was something to do with the white light Locke saw when he looked into the eye of the island way back when.