Sadie and Chewy both honk when they get excited... I was told this is reversed sneezing. If I cover my hand over their nose it stops...(I guess they breath through their mouth and it helps?
) For what ever reason the covering their nose works for us. As soon as it stops i take my hand away. I have to do this a few times during an attack because they always start back up again. After a few min they calm down and we can continue walking. (Chewy always does this when he meets other dogs)
Try not to get him excited about going out, this may keep him calmer.
I also have the kind of harness you are talking about. Try turning it around, it could be you have it backwards... It shouldn't be too high up on his neck. I can't see in the pics...