Here's my version of a plinth. It is resting on an 18" thick footer which you cannot see in this picture. The pin in the middle of the plinth is poured in and keeps the post from shifting. I actually welded a stainless steel cap on this plinth before setting the timber post upon it - so termites couldn't make a sneak attack through a potential crack in the plinth. Yes, the stainless would probably be considered overkill.