skip the concrete, use something that will last. Granite blocks, you are in NH after all, Swansons on 101A in Amherst has an "economy bird bath base" its a 10x10x10 granite block, we have them drill a hole in one side, then a matching hole in the bottom of our post. Drop a rod into the granite hole and your post on top of that and you can't knock it off the granite.... of course if you're raising bents this won't work, but if you assemble a piece at a time this works slick. Again, being a granite stater I imagine the "soil" you're putting it on is probably gravel anyway....
