Depending on how the contract is constructed, it is possible to avoid any liability.
"This FRB note can be redeemed for 20 ounces of gold, pending availability*."
*Our bank only holds %10 of all outdtanding notes as reserve in gold at any moment.
There is nothing wrong with a person lending money to the bank and owning debt, or depositing money in a bank account and owning money that can be withdrawn on demand. But it needs to be clear which the bank customer owns: money or debt, as they are very different things.