I’d bet it’s this little bugger " : "

It is for me.

This is such a spot-on response. In addition to another in this thread (stating you are allowed to and should control the situation), it’s 100% acceptable for a dog to correct another. Some dog owners see any “bad” interactions as aggressive but dogs can’t learn to interact well without correcting each other. Unless it escalates into a legitimate fight, they should be allowed to work it out.