IMO I'd only raise with A9o in late position if I have observed the table enough to steal my oppenents blinds (If it's a substantial amount). Other than that I'd fold preflop. I wouldn't bet with it post flop with no kicker though. If it's checked to me i'll gladly take a free card. If not then maybe I'll see the next card cheaply or i'll muck. Your opponent did get lucky on his draw. But I think its more important to prevent those situations of being unlucky. Going to the showdown with A9o is hoping for a prayer.