If you have a Post hole digger drill 4 holes and put a bag of Sakrete in bottom of each at 2-3' down, insert a J hook bent rebar or two in each and fill in. 4 60Lb bags are $5 each.
Or you can do a star pattern with three rebar pounded in at angles thru the bottom plate.
He is in Vermont. The frost will grab the concrete and lift it. Better to use Sonatubes, wrapped in plastic. Or cut the end out of a 5 gallon bucket and slide that over the piling so that frost will move that instead.