I agree with everyone else. I have read lots of stories and experienced myself the need to pull them back/up quickly in an emergency situation and a harness pulls on the right places, as opposed to a collar. One time could be extremely damaging. Letting him wear it in his comfort zone (crate or such) and giving him treats while he's wearing it and moving slowly to walking on it should remedy the situation.
Good luck with your handsome boy!

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