I'm conditioning Carbon to a 'don't eat icky stuff' muzzle at the moment. When I discussed his rampant kelp eating with my trainer this week she said, "Use a muzzle while you work on 'leave it' and 'drop it'". My immediate reaction was "but he doesn't like it". And this coming from someone who had a dog who, because of his breed, had to wear a muzzle a LOT and did so happily.
Anyway, my trainer and I had a long discussion about how to get Carbon to love it. All of which I already knew, but where I fall down it doing things in small enough increments and moving from indoors to outdoors (two very different contexts for a dog).
So...for you, great news is that Ripple has already successfully worn the muzzle indoors. Now you need to break down getting that outdoors by very small increments. In the meanwhile, that means walks on pavement, on lead and away from green areas where yummy things are just waiting to be gobbled up. It's a complete pain in the backside for us humans, but it has to done.
I'm feeling your pain right along with you!