I've used 1/4" (or bigger)steel kerf plates let into a mortise cut into the end grain of the post with a chain saw plunge cut, then through bolted & plugged with wood plugs. Also, I've seen, but not used, engineered connections using a threaded rod inserted into a slightly oversized hole in the post base, with the space around the rod then filled with epoxy though an angled access hole (1/4" +/-) drilled through the face of the post. Either way you'll want to engineer your connections. I often use black roofing cement to seal the bottom of the post, with a piece of pressure treated plywood for a bearing plate.