When we have room in our family for another dog, my husband wants to get a Dobie. I too am concerned about the size more than anything. I've owned big dogs in the past, and they can most definitey be trained well, but dogs play, and chase each around and have fun! I don't think that I'd be comfortable with a dog that big playing with my Yorkie, even if it was my own. So yeah....I think that me and my husband have to have "words". He loves Missy to death though, so I know that I'll win
My brother owns a female Dobie. I haven't met her, but she seems like a great dog. I'm sure that it can be done. Look at Cesar Millan's "pack". They are all sizes! I'm sure a Dobie and Yorkie could be trained to live together just fine.