It has become obvious that we cannot ensure that Blacklash and Hematus will remain imprisoned in Lethlor. That black dragons have taken up residence there, and that the ogres managed to steal the Sign indicates that more drastic measures will have to be taken.
The drakes' prison is maintained by three runestones that may only be retrieved using the Sign of the Earth. Those runestones can then be used to break the seal which imprisons them.
