Contractor overages

[Ray S.]

I've been doing a rental property rehab. The contractor hasn't come close to meeting any of his target dates, and has gone over budget many times. What is the best way to keep him on track and hold him accountable for overages? In my experience withholding payments just keeps them from working, what else can I do? I do have a clause that he has to compensate me if he goes over, and he is at that point, but I know contractors will always try to get out of that, so I know I won't get that money back without a fight. 

Also, is there anyone I can hire, like a consultant, to bring in that could oversee his budget and see if his numbers for what he's charging are reasonable or not? And if they aren't, how do I renegotiate after he has already started?