Demurrage can't work in a bitcoin-like cryptocurrency without breaking something.  I've looked pretty deep into this before, and wish I were proven wrong.  So far, it just adds too much complexity or it fails to encourage the desirable activities such as deliberate consolidation of inputs.  One thing that could be done is to add a new rule to the minimum fee structure that adds a relative increase in the minimum fee after a year or so, in such a way that long term savings accounts end up paying for their past security eventually; but that's not really demurrage and doesn't contribute much to consolidation of the blockchain nor does in contribute anything to the running security.