Looking for masonry advice!

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I need to install a square fence post (8×8 cm / ~3×3 inches), 2.3 meters tall (~7.5 ft). My problem: the post cannot be centered in the foundation hole which is 30 cm in diameter (~12 inches). It has to sit deliberately off to one side, 5 cm from the edge (~2 inches) (see diagram). Concretely, on one side there is only 5 cm of concrete between the post and the wall of the hole, and on the other side about 17 cm (~6.5 inches). To hold the post in position while pouring, I'm considering two opt...