Maybe this weathered old hard wood is extra tasty to carpenter bees because nothing seems to discourage them: bee killer, spray foam, canned air. If you plug up the hole, the eat it open again. If you kill one, another takes its place. So mostly what we rely on is just swatting them with a tennis racket. Once they've been hit by that, they know to take off as soon as you pick it up, though (they're smarter than they look, these bees!).
They are very territorial, so once they move in for the season, they try their best to keep us away. One of their favorite intimidation tactics is to hover about chest level right at the top of the steps, so whether you're coming up or going down, you have to face the wrath in order to pass. But even just sitting in a chair on the porch, as I was this evening, they harass. They like to hover about two feet away from you for a bit, then start doing close-proximity fly-bys. Very annoying.
This is the bee who was menacing me this evening:
Fresh gnawings below the hole he was protecting:
Here's the hole (you can see another bee in there):