Select 2 blocks with Wooden Axe and then create zone by
You have 3 options in the Zone: Strict zone, Interact, Mob Spawn. You can change them by the commands:
What do they do:
Strict zone disables any setBlock and destroyBlock methods in your zone, by that you can protect your zone even from such things as Nuclear Bomb from Alex Caves or some bosses from Cataclysm.
Interact defines if someone else should be able to interact with chests, buttons, doors etc.
Mob Spawn defines if any entities can spawn in your zone.