Limit government spending to a percentage of GDP
How about something like an amendment stating "Congress shall incur no debt which shall cause the total obligations of the United States to exceed 110% of the gold physically in the possession of the Treasury." (There would need to be a few other sections, like one requiring an annual accounting of gold in the treasury's possession, and one which would cause any government employee/agent stealing gold to [a] forfeit all retirement benefits, [b] be terminated from their position (life appointment to the supreme court notwithstanding), [c] restore back twice as much as was stolen to the bereaved upon conviction by a jury.)