Into the winecellars once more
"Hmmm. I can lock this, or Oly can, but if the trolls have a key, there's nothing to keep them out but the ogres -- and another battle down here wouldn't be desirable. Even jamming the lock shut might not help; the trolls seem to be artificers, and might well be able to dismantle the lock if they can't unlock it.
"An elementalist, or a gang of masonry workers, could back up the grate with a wall. At least that would give considerable warning if something or someone tries to come this way."