Ruby and Cassie are SO much better! Now that I've recovered from the most recent (rather annoying) surgery and my son has repatriated the puppy, the worrisome behavioral issues have pretty much resolved.
Putting Ruby on a leash or confining her inside a room with me and Cassie all the time she's in the house worked some sort of a miracle in short order. Really, I couldn't begin to explain why or how this worked...only can report that the competitive "I'm gonna kill you if you look crooked at me one more time" behavior has completely stopped.
Tying Ruby's leash (it's one of those long nylon training things) to the stove handle at feeding time has been huge. Our routine is now as follows:
1. Prepare each dish of dog food.
2. Secure Ruby out of reach of Cassie.
3. Place Cassie's food in front of her, where Ruby can see her and Cassie can see Ruby.
4. Ask Ruby to "SIT." She does this readily, thank goodness.
5. In response to a successful "SIT," place Ruby's food in front of her.
Cassie no longer runs away from her food when Ruby is in view. Apparently she realizes that if Ruby is on a leash, she can't run over and grab anyone else's dinner. Cassie will lift her lip at Ruby if Ruby manages to insinuate herself while there's still actual food on the plate. But generally both dogs occupy themselves with licking up every spare molecule (this process goes on for quite some time after any food visible to humans has been consumed), and neither pays any attention to the other.
Ruby and Cassie have stopped fighting over chew toys. As we scribble, Ruby is quietly exercising her new teeth on a chew. Sometimes she wanders off, and Cassie does NOT run over, grab it, and carry it into the office, there to guard it with her life.
The two-dog walk is working pretty well. Yesterday morning Cassie couldn't stand the thought of being left alone while Ruby went out first, so I took the two of them with me on a tandem leash for the first mile (about as long as Cassie can stand), then brought them back, left Cassie in the house, switched to a single leash for Ruby, and walked about a mile and a half with her. Last night we returned to the tandem leash for an evening walk of a little over a mile and -- get this! -- Ruby did not drag at ALL! She walked right along with the leash at slack, just as if she had good sense.
So Ruby is learning to heel nicely, Cassie is getting at least a mile and, now that the weather is moderating, often two miles a day, and Ruby and I are getting the required minimum two miles I'm supposed to be putting in.
I suspect probably the source of the problem was that I was too sick to get out of bed and there was no one else in the house to wrangle dogs. My son relieved that to some degree by removing Ruby temporarily, but because she can't hold it a full four hours, he complained that she defiled his house. She defiled the floor even when he left her in her X-pen while he was at work.
He normally races home for lunch to let Charley out, and since he's a large, mature dog, that presents no problem in the toileting department. But Ruby is still fairly small, and she's only provisionally house trained. She hasn't had any accidents here, because I'm here all the time and can see when she starts to squirrel around wanting to get out.
It's 9:45 and still cool enough for a doggy walk -- sumer is y-goin' out, lhudly sing hot diggety! -- and so I think it's time to exit stage left...