My suggestion is to rip the deck out and rebuild it using cypress. Bugs don't like it. My deck has been there for 4 years and I've never had a wasp nest built anywhere on it or under it. Carpenter bees stay away too.
A side note about carpenter bees, for those of you who have been chased around, or even off the roof, by them....The one that is agressive is the male bee (two will nest together, male and female). He will get in your face, buzz all around you, etc, if you get near the nest. You'll often see them hoving around near the roof or eaves where the nests are built. However, he can't sting you. He has no stinger. The female is the only one with the stinger, and is quite docile. She usually won't sting unless molested.