What are the best ways to manage challenges to the storyteller?
For my money the simple thumbsup system works with my group. You're welcome to tell the story and if someone contradicts or uses a card for a nonessential element you call an audible and stick out your hand thumbs down. You have about five seconds and then everyone else joins in thumbs up or thumbs down. Majority rules.

The rest of the time if the story teller is rambling you can just stick out your hand thumbs down and as they go if more people join your thumbs down and it reaches majority then you lose and the story passes on.