Not sure it's even possible to achieve being "completely free of corruption from moneyed lobbying", but at least getting to a system where the legislature or whoever has the power and the will (if not absolute mandate) to continually evaluate the situation and combat corruption (sanctioning, suspending, or expelling violators; penalizing lobbyists who don't follow the rules; amending the rules as needed to keep ahead of the problems).

There's just not enough real consequences for any of these people failing to live up to the standards we should expect of them.