Over in the World many of us use deck foundation blocks, mainly because a lot of the landscape in Canada either moves around from frost heave - temperatures from -30C to +30C will do that. These items are roughly pyramidal in shape, but with the top chopped off, and have a set of cross slots to take wooden sections of 2/3/4" square. Ar around 50 - 60 pounds weight, they are not going to wander around much, and the vertical hole, again, to take 3" or 4" square posts, is as vertical as the base is flat.
Lemme see if I can find a pic.
tac
OVGRS