Dean was not unlike one of the Greater Dead of my world, when he was what you call a demon. The Mark seeks to corrupt a soul further into Death. It can be transferred between souls, but not into stone or metal. It cannot be broken, not without risking releasing the Darkness, or perhaps it cannot be broken at all. You've had others try, haven't you?
Transferring it to one of the Dead is an option I can offer you. I can't guarantee it will work. But I also can't see why it shouldn't be possible.