onBlockDamage not repeating?

I'm trying to intercept player interaction with blocks continuously. Ie, when they are smacking something, I want to get a damage event every time they hit it (or every time damage it applied I guess). But it seems like I only get the initial event. Same goes for the onPlayerInteract event as well.

Is this just how things are, or is there a way of rigging it so that I get periodic messages?

Actually, for what it's worth, it also seems like setting the event to cancel = true doesn't seem to have any effect. Damage still continues to get applied.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.