Ground contact wood in the south has a very short life. I don't know how many fence posts we replaced over the years.Termites. or ants. or dry rot.
All of the above?
Had to replace the 8' dia round end post. Now using a pair of pt 4x4's tied together w 2x6s, and 200# of concrete. The fence it supports is only 350' long, should be sufficient.
When we set posts now with concrete, we make sure there is a collar of concrete 1-2 inches above the ground surface. We've had so many posts rot and break off right at the surface of the ground. The collar of concrete seems to really slow this process down. We set some 6x6 posts for a shelter and my greenhouse. We made a wood form around the post and filled with concrete. These have done great.