Got schooled on post hole depth at a job in Duluth last winter.
We were setting a line of cedar posts on a slope, ground was half frozen. I was going by the old 'one-third in the ground' rule. The homeowner, an older guy who used to build docks, came out and said, 'You're gonna get heave. Go another eight inches, hit solid.' We argued for a minute, but I did it. That extra depth made all the difference come spring thaw. Anyone else run into a local who knew the land better than the book?