What form can I have a contactor sign stating that all subs and materials have been paid for prior to making my final payment so I don't get surprised with a lein for upaid items and services?.
If the project is an owner occupied residence, you are protected from subcontractor/supplier liens IF you have paid the general contractor for that work and have not received a lien notice (KRS 376.010(4)). In that case, a lien release from the general contractor acknowledging that they have been paid in full is sufficient to protect you. But, the legal requirements of the owner-occupied exclusion can be tricky.
Otherwise, you would need lien releases from all of the subcontractors and suppliers to ensure that a lien could not be filed.