Here's an idea I had: make the Totem for a Tribe be a Bank. The area controlled by the Tribe is controlled by how much stuff is in the bank. The bank could robbed by PvP players. Here's the details:
1) the Totem serves as a storage bin for the Tribe, the Tribe's bank
2) the area controlled by the Tribe is based on the contents of the bank
3) Tribe members place/contribute to the bank, thereby growing the Tribal area
4) enemy players, outlaws, could rob the bank, by coming onto Tribal lands and looting it
5) Tribe members cannot be attacked on their lands, but their bank can be looted
6) if a Tribal member tries to attack the bank robbers, they become PvP enabled, so the bank robbers can fight back
7) Totems and villages cannot be destroyed, but they can be looted.