The Fence panel is non-structural so it does not require any engineering.
Typical fence panels are 4" thick with chamfered edges
Typical posts are 12" x 12" with "notches" in side to allow for fence panels to sit in them.
45 MPa design, 200 +- 20mm, 4-7% Air entrainment, Type 10 Normal Cement
Typical fence panels have a "board-form" finish on one side and either smooth or striated broom finish on the other with smooth bands around the edges
Some FENCE panel projects: