Thanks to all who have responded thus far. It seems like the
conscensus is to either lap joint or pour up the footing after cutting
off the bad wood in the post. I'm going to consider the second
option--not one I had thought of before--because it sounds like an
easier way to go than having to lap and lag a joint. I have since
checked the other two posts along the side where I have the problem,
and found that they too are in poor shape, so I think I'll have to do
whatever I do to all four posts, one at a time. If I opt to pour up
the footing, what sort of bracket do you recommend which will both
allow for a secure attachment to the remaining post, and allow the
post to slide into the bracket to secure it?