Reputation-based gold storage

In order to preserve the right of people not to be deprived of the value of their money without due process of law, a polis may consider two currencies for their polis. 

1. Gold: A store of value
2. Silver: A medium of exchange. 

The key is that a Polis could tie up the amount that a person can save as gold with their contribution to the community to create an incentive structure.