Cement will cure just fine, even under water. I, however, am not a fan of planting wood in concrete. The builder of my home put fence post below grade and did the fill with cement. They're now decomposing. Now I have dig up a big block of cement, as opposed to simply digging a new post hole.
I do have some decking post attached above grade to anchors embedded in cement. They're holding up just fine and will be a snap to replace should the need ever arise.
Last edited by 1minute; 05/29/20.
