In western Ks where I’m from originally, they used to use limestone posts. They don’t rot off. Back in the late 1800s when that area was settled, trees were few and far between. So they improvised and quarried limestone posts. They’re generally not very uniform in size, but about “10 square, I’ve helped move and set a few. They are heavy SOBs. But last forever. I have some land in west central Ks that I would like to fence with them, but it’s way too much work, and I don’t know where one could get them in quantities these days.