Heh, well in the case of Swordfell, I would have explored other options before exiling him.
I speak as someone who has had to play with difficult dukes. But, you can hike taxes to 50% (is that the cap?)
The capital of Swordfell is in Balance's retreat right? If the Courts of Iron duchy really doesn't want to be tied to the Courts of Stone can't it split off into its own realm?
