I don't rack to a secondary fermenter unless it's going to be longer than four weeks. As such, when I dry hop there is still plenty of yeast in suspension, which will overwhelm any nasties that might hitch a ride on the hops. When I'm ready to clarify, I rack the beer off the hops and yeast cake, rest it for a couple days, add my clarifying agent, rest another day, and then keg. I haven't had an infection problem yet.
th Cap'n in Portland, Oregon