Your right he would be for the market deciding what form of currency was best. A company issuing a currency would have to uphold there contract with the person trading goods for the currency ie having the specified amount of metal in there coin. If they breached there contract and the courts would then have a role enforcing contracts. Currencies could be anything (nails, cows) whatever currency had enough demand to sustain. My opinion would be never allow government to issue a currency even with competing currencies. The table is lopsided immediately with government being the apparatus to enforce its own contracts.