I'm digging two post-holes for a gate re-build project and I've run into a problem (these will be the 4x4 support posts). One of the holes went great...down 18" no problem. The other hit solid stone about 3" down. I've tried to look for the edges, hoping I could dig it out, but it looks big. Any ideas about getting through it, or working with it? I had a thought that if I could anchor the 4x4 to the stone, it would be like sinking it in concrete...or is that crazy-talk?