I recently moved into a house with a wood shake roof. Apparently, at some point in the past, some of the shakes must have started to lift at the bottom so the previous owner drove nails into the shakes a few inches from the lower edge to tack them down. Now some of these nails have backed out and are sticking up from the roof surface. I haven't noticed any leaks yet. Given that this damage has been done, what should I do? Remove the nails and patch the felt with roof cement? Insert shims? Drive the nails back down? Any advice would be much appreciated.