I have a slim German 16Ga hammer gun that I use for all my less than duck sized bird shooting. I cock hammer when approaching the dog and the second after the first shot. It sounds like it would take along time but after you practice it a bunch it's as quick and natural as clicking off the safety or shifting gears in a car or anything else. Get some snap caps and just make it a point to practice the firing cycle a dozen times every day. It only takes a few minutes of time.
I started out cocking both hammers at once and got to where I could do that naturally and quickly too. My problem was remembering to uncock an unfired barrel. (as has been mentioned) After I caught myself walking around with a cocked gun a few times I changed my method.
