I wouldnt use the landscape timbers for the above reasons, especially rotting and warping. When a post is sawed to a flat side, it cuts the grain and fibers and lets them rot alot faster and reduces their strength. Another name for the posts you guys are talking about is Hedge. Around here there are 4 inch hedge posts that have been in the ground 50 years and are just as good as ever. A nice 12 inch hedge post will last far longer than a person will live. The problem with them is after they season out, they are just like concrete and you cant drive a steeple in them and they wont hold a steeple. There is no corner post that I am aware of that will equal it unless maybe 8 inch well casing pipe. We would cut out hedge fence rows on the shares as Springfield Mo was growing and the housing developments would take over. When they were green you could sharpen them and no matter how crooked they might be, you could still drive them in the ground in rocky soil and they would never split and they last forever, it seems like