Hm. Is a problem building, or is this a passing phase?

Now that Ruby the Corgi Puppy is getting to be about the same size as Cassie the Corgi and is filling out and looking like a grown dog, Cassie is beginning to show considerably less patience with her antics.

Of course, from the git-go she has "corrected" anything that was truly annoying with a fake "bite" (I've gotten in the middle of this once or twice and learned that the feint doesn't involve closing the jaws but is actually more like batting with the side of the canines). Sometimes she demonstrates her annoyance by silently lifting a lip to display the (not very) threatening fangs. Sometimes she  has tolerated things that, if I were a dog, I wouldn't put up with.

One such trick is grabbing Cassie by her thick fur ruff around the neck and hanging on. Ruby especially likes to do this when Cassie comes over to me for attention and loving-up. For months, Cassie has tolerated this little shenanigan. But no longer!

Over the past week, we've had a couple of Events that were pretty alarming, from the human point of view. 

Something -- fairly minor, from what I can tell -- triggers Cassie and she turns on Ruby with an angry growl and what appears to be a serious intent to do damage. Ruby yelps and, heaven help us, returns fire! So now they're both growling and thrashing around.

So far, no biting has happened. I've always been close by, and when I holler KNOCK THAT OFF!!!!, they immediately stand down.

It may be pack dominance behavior -- Ruby may be getting to the age and size where Cassie has to get a lot more insistent about maintaining her throne as Queen of the Universe.

Something similar happened when Charley the Golden Retriever was growing up at our house -- throughout his puppyhood, I would babysit Charley while my son was at work. When Charley reached about the age of six months, Cassie, who had put up with a phenomenal amount of puppy silliness, suddenly decided enough was enough.

By this point, he was much bigger than her. She flew into a high rage several times, emitting quite the menacing effect. She never bit him, but you couldn't prove by me that she wasn't about to.

Charley, who lacks quite a bit in the intellect department, was quickly trained by these scary threats, and peace soon returned. Also Charley started to behave a great deal better all the way around.

Ruby, on the other hand.... Yes, Ruby.

Ruby is no calm but doltish golden retriever. She is very smart, very determined, amazingly energetic, and not about to be told what to do. Nor is Ruby a six-month-old puppy -- she's over a year old now. And she certainly is capable of holding her own against Cassie, if she decides to do so.

And therein lies the question: Will she decide to do so?

Ruby goes in her crate whenever I leave the house, so there's no risk of a dog fight happening when the referee is out. But...the referee would prefer not to get into it with 25 pounds of muscular dog armed with long pointy things. Make that 50 pounds: 25 x 2.

What d'you think? Is this the normal interaction of an older dog showing a younger dog where its place is? Or could we be developing a problem here?

If the latter, is there a known strategy for nipping it in the bud, before it gets serious?