Spending by "super PACs" is a direct result of unrealistically low contribution limits. It takes a lot of money to run for mayor of Los Angeles.
The only way to stop PACs is to lift the limits on direct contributions. Then the money would at least be traceable and the candidates accountable.
The PACs are running campaigns and crafting messages beyond the candidates' control. They are the direct result of misguided reforms that have simply driven the money underground.