I had a general contractor work on finishing out a basement. Things were going decent until a subcontractor showed up to my house asking if I had heard from the general contractor. He informed me that he hasn't been paid for work. He also informed me that he did not have a contract with the general contractor so he was really just trying to get in touch with the general contractor. We are approaching the time schedule for the final 10% retainage being paid. How do I go about protecting myself from subcontractors filing liens on my house in the off chance that he has done the same to someone else?