yes i would do the nothing is free 100% of the time, also if he is already sitting before dinner than change it & make him lay down instead, or shake paws, anything as long as he has to work for it.

Also like stated before I wouldnt drag out the punishment all day long just catch him & discipline him withing a few seconds of the act & do not drag it out longer than 10 minutes or so. Then make him obay a command & then release him from punishment.

Personally sa far as the snapping thing I would of dragged him off the bed right away & made him lay on his back while I kneeled over him making him in the most submissive position.

Like you probably noticed, (he did too), you thought he was progressing so you let you guard down a bit he saw this as a perfect time to challenge you. I would continue with 100% nothing is free for at least 6 months or so before you go back down to 75% of the time. No matter what always continue this for the rest of his life, yes you can eventually lower it but never stop it for good.