That head knock out with debris really bothered me, too. I do understand that the writers didn't want Odo to be indestructible, but having him KO'd by a blow to the head seemed very contrived to me. I also agree that if he had lost consciousness, he should have dissolved into a puddle of goo, not remained solid.
On an unrelated note, I was very
glad that in that episode, they decided to send the kid and her father to live with the Vulcans. The thought of Odo having some alien kid tagging along after him and keeping him from being too lonely made me gag. It would've been the equivalent of the baby effect on so many previously successful shows that die agonizing deaths after some nimrod decides a cute kid will boost ratings.
EDIT: That airlock business bothered me, too. If Odo could get through it, you'd think that air could, too!