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A vest for cue working mode is added the same way all other cues are added.
When you can reliably predict your dog will be in working mode in a public place (and are willing to be $100 that he will go into work mode), then you add the cue of the vest or bandana or special harness. Put the vest or harness on just before going into a public place where the team will be working.
Then, your dog will start to associate putting on the vest or special harness as the cue to work. It's based on classical conditioning or pairing of the new cue with the behavior the dog already does. The fact that the equipment feels different than what the dog usually wears will help her understand this job is different.
You can certainly help him to be comfortable in the vest at home but if you want it to mean something, then wait to add it to 'work' situations.
Read this post on vests
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