Actually, I think you'll have a pretty good response from your druid PC if you bring out a "Blade" style adamantine containment "suit".
i.e. Steve Buschemi's character from "Con Air" being wheeled out in full "Scary Prisoner" attire.
Not only will it keep the character imprisoned, but if you roleplay the guards/NPCs as truly terrified of the druid's potential, then it will also lend a sense of empowerment to your PC...making them not only open to imprisonment, but actually pleased with the portrayal.
Just a thought.