With the barking when you get back (which I assume is excitment); I would go as far as to, as soon as he barks, turn around and walk out of the door again and only return once he has quietened down.

What you are doing sounds brilliant, particularly rewarding him for being calm/quiet.
Poison girls idea of giving him something to do (give him a toy- maybe just lob one for him to catch, if he's got a toy in his gob it'll be harder to bark )

How did you get on with the food change?

Best of luck with the headcollar and heelwork training and keep us updated

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