6E1 p.379
"A character must define one way in which other characters can destroy or unmake an Unbreakable Focus. This is usually connected with the Focus’s origin in some way. For instance, many magical Foci are considered Unbreakable, but the person or being who made the Focus could probably destroy it. The GM should be careful with an Unbreakable Focus; if he destroys it, the character should have some way (a quest, perhaps?) to remake it. Of course, Unbreakable Foci can always be stolen, even if they can’t be destroyed"