below level which sort of correlates to discussion of a microbial active level, that is, around ground level, you're suggesting just go ahead and flex seal from (four inches above) ground level and everything in the ground. 8' post will stick 24" in cement (the hole might be 30") It's not going to be heavy duty though just want to hold up a lighweight gate that has mesh to allow light to go through type stuff. rest of 6' fence will just be 2x2s.... So, not too worried about having to replace it every ten years...heck, I might not be around in ten years.