We left them on them when we took them to the doggy park early this a.m. and Murphy let out 3 separate barks all at different bigger dogs as they entered the enclosure, and each time DH and I are cracking up at his reaction, but he shuts up right away each time, which is the point.
At one point I felt bad for him cuz he was under my chair and his face looked as if he was saying " pfft! I give up! " One of the other owner's said she only had to use hers for her one dog for a short time, it was a behavioural tool that curbed his barking, so I am hoping I can at some point stop using them.

