Battle of thrones how to defend without shield in throne area?

To avoid losing resources: consume them before the event starts by upgrading things and keep your stock bellow protection cap.

To avoid losing troops: If you are about to be attacked by someone you know you can't win against, send your troops away to gather resources/kill monsters or remove them from the garrison so the won't engage in a battle to protect your city. You will lose city valeu, but your resources and soldiers will be spared.