Two of our dogs got into a fight today - the Shih-tsu and the Border Collie
The BC is our alpha, but is aging pretty quickly and has lost a few steps. The S-t is generally just playful, but has a fuse that has burned down more than once.
Today, we all went to Petco, the three dogs on leashes. They picked out a few toys each (all on post Christmas clearance!). When we got home, the toys hit the floor.
It seems there was too much excitement. Long story short, the BC and S-t got into a serious fight. Biting and snarling. The little one was not taking any shit from Mama, but Mama bit her ear and drew blood. A lot of blood. The little one would not back down at all. Her 16 lbs was standing up straight and loud to the BC's 60 lbs., bloody ear or not. There was blood on the carpet, the floor, the sofa, the wall.
I grabbed each of them by the collars. The BC slowed a bit for me, but the S-t wasn't stopping at all and bit at me but couldn't connect.
A few sharp "NOs" from me slowed them down enough to be able to separate them.
The little one's ear was cut and bloody, but no serious harm.
Hours later now, and there is an uneasy wariness in the house. The two combatants are eyeing each other every now and again. There have been a few growls.
The poor GSD, who is the gentlest soul to ever walk the earth, is beside herself, not knowing what to do. She is clinging to me like static charged Saran Wrap.
This better blow over. The little one is challenging the BC.
That isn't smart. The BC has always been wrapped tighter than a drum head.
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Clyde just loves everybody. Bonnie is the sweetest little lover dog you have ever met...until...she gets around other female dogs, then, OMG! She does not care what size they are! Sge turns into a Tazmanian devil. It's quite amazing to see.
Here they are. Bonnie is on the arm.
I like the cut on the one not on the chair arm. We keep ours similar to that, but with a longer top and a silly top knot that looks for all the world like a hair sculpture of a whale's spout! 
They get to the vet far too often. The BC has been there a lot for various geriatric issues and the little one goes in with whoever else is going so the vet can weigh her. I'd bet each of our big dogs has seen the vet a half dozen times this year, and the little one has been there for each of their visits plus her own.
We are going to ask for a fleet owner discount next year.
True, they'd all just come back from the PetCo and were pretty excited.
The thing is, the Shih Tzu (my "Baby!"
never tries to take anything from the Boss -- toys, treats, food, nothing. In fact, she goes out of her way to avoid walking past her unless there are four or five feet between them.
The Boss BC is easily startled, and she bites. She's bitten a groomer who started the dryer from behind her, Stinky Jr. when he suddenly appeared on a dark summer evening, and other dogs. But she's also just attacked other dogs for no reason we can see.
Today, not for the first time, she snapped at the cat, who also wouldn't be interested in her food or toys, but may have gotten in her space. (She tends to lie down in doorways.)
The little one gets very defensive, though. She tries to stand her ground and doesn't back down. But she can't really defend herself when she's a fraction of another dog's size.
I was just so horrified to see her bleeding so much!! And I was scared about whether she had any internal injuries. She seems okay, but I'm just nervous about it now. We'll definitely talk with the vet about it.