I had posted just a bit ago about getting a recommendation on a dog breed. Maybe I should back up and ask another question first. Should I even get a second dog?

I've just read the article on raising 2 pups together and I believe Ed is right. The article focuses on raising two pups together though. In my case, I have a "not-puppy" and am looking to add a second dog.

My first dog is a 7lb Shi Tzu. She's reasonably well behaved, but hasn't been through any obedience program. She does come when she's called. She'll sit when told (but not stay). She doesn't exhibit any dominance issues at all. She's really everything you could ask for in a lap dog -- which is how my wife treats her and what she wants from a dog.

Our Shi Tzu mostly has free run of the house. For the first 6 - 8 months we left a lead line on her all the time though. We also kept her in our sight all the time. We have a crate for her. When we leave the house, she's in the crate. She sleeps in the bed with my wife and I though. Someone is home almost all of the time and she's given free reign. Mostly she sleeps on the couch if she's not playing with someone.

Our Shi Tzu responds in mixed ways with other dogs. There's a maltese next door that she plays with all the time no problems. Sometimes she greets other neighborhood dogs just fine when we're on walks. Sometimes she shows fear and extreme submission. We're always quick to pick her up in those situations. I don't know for sure, but she seems more comfortable with calmer dogs and less comfortable with high energy dogs. Although when she plays with the maltese next door she's pretty high energy with that dog.

My plans for the second dog is to also crate train it. I'm not sure where I'll put the crate. Our Shi Tzu's crate is in the living room. I plan for the dog to eat and sleep in it's crate. Our Shi Tzu eats in her crate. I plan on keeping the new dog with me any time I'm home and in the crate otherwise. In fact, I may just put the crate in my basement office.

What I'm looking for is a "medium" sized dog. I don't want it as a companion for the other dog. I don't really care how much the two dogs interact -- the less the better I guess. I suspect though that I'll have a hard time keeping them completely separate as they'll both be in the house together during the day.

Doug, I think the second guestion is the most important. "Should I get another dog." Only you can answer that pressing question. I commend you on your thoughtfulness of the family dynamics and how a new presence will be an impact on it. There is no way the status quote can not be changed.
Any dog is going to react differently to stimulus on nuetral territory and what comes into home ground, so to speak. Will there be pack issues? Yes, I think so. Will they be resolved within the pack? Yes undoubtedly, one way or another, but it's up to you as how those issues are resolved. Ed Frawley has real good things to say about this, and he's a much better communicator than I am. Take advantage of his largesse.
Lastly, perhaps firstly, how does the rest of the family feel about it? As a previous poster noted, consistency and patiences are the most important aspect of training after technique. Does the family buy into the change? And make no mistake, there are difficult times to come if you make that change.
Keep up the good work!
Do no harm,
Randy