Stop counting his booze, stop looking for bottles. Stop marking a calendar every day he drinks. You keep making all these "rules' - it isn't working is it? Threats don't register with an A - they don't care. It only forces a game of cat & mouse him trying to outsmart you with his drinking, and you trying to show him that he can't by proving to him that you know.
Lexie is right - you should never utter an ultimatum until you are ready to enact it.
Yes deciding you will no longer live with an active alcoholic is a boundary. Stating that you will leave the next time he drinks is a failure of that boundary because - he will probably drink today, and you have already stated that you cannot leave right now.
Shift gears a little. If your boundary is not living with an alcoholic, and you can't leave because of financial reasons, then get busy planning while he is getting busy getting drunk. What financial resources do you have? What can you do to change this situation so that IF you decide to leave that you can?
Disengage with the A, stop arguing with him about his drinking - stop trying to prove you know, stop thinking there is a logical cell floating in his head that will magically one day agree with you, stop expecting a different outcome.
Great that you are headed toward Al Anon - keep posting, keep reading, keep educating. Take care of yourself and you son first and stop worrying about AH. Once you get that concept, even while living with him,it will be a much better environment for you.