In this video by Dogmantics, dog trainer Emily Larlham goes over some beginning exercises on how to teach your dog not to bark while on a walk.
"Barking can be reinforcing, so the more a dog is allowed to bark the more likely they will continue barking in the future. When you and your dog are surprised on a walk and your dog starts to bark, simply say "Let's Go" and move briskly in the opposite direction. You can use this cue whenever you change direction unexpectedly or need to move from an area that is causing your dog to be over their threshold." (Dogmantics)
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