I use a variety of behaviors that I can teach separately and then combine them for a successful stack (I've shown chows in conformation, not shepherds, but the concept is the same).
First thing I do is teach my dog to look at my right hand when I hold up my forefinger. This gives her a focus point. I just raise my finger, mark (either with a verbal "yes" or a click) when she looks at my finger, and then reward it - gradually extending the amount of time before I give the marker/reward. I want my dog to watch my finger for a good 30 seconds before I add it into the stack.
Then I teach a stand. I walk the dog forward as if we're doing some gaiting, then I turn my body slightly toward my dog, raise the forefinger and gently apply backward pressure on the leash while saying "waaait". I don't use my stand command on this because I do obedience too, so I teach "stand" separately. You could certainly use "stand" if you preferred.
When my dog stops and looks at my finger, that gets the "yes!" and reward (which is in the right hand).
Once I have the focus and the stop/stand, I work on the placement of the feet. I do the front feet first - I start to only reward when the feet are square. I also teach my dogs a "paw" command which means "move this paw" and I touch the paw I want moved. And I teach a "scoot" which means "take a step backward" as that helps rock the chow back onto the hind legs a bit (they're supposed to stand square).
Once the dog is moving into a focused stand with square front feet, I concentrate on the hind feet. My eventual goal is to have a dog that, on signal and/or verbal, walks into a perfect stack.
Another great thing to teach your dog (eventually) is to focus on the judge. You use a separate command, like "look". You need two people for this - one person as the judge (with the treats) and then yourself with your dog. Tell the "judge" that when you say "YES!" (or click, if you're using a clicker) then they're to give your dog a treat or two. And then walk your dog up to the "judge" and wait for her to glance at the judge. Immediately say "YES!" (click) and then the judge will hand your dog a treat.
Circle back around a few feet, do it again. You'll usually find that after a time or two, your dog starts to really look at the judge (don't be holding out your forefinger on these as the focus should be the judge and not you). When this happens, start saying "look!" as you circle around to head back toward the judge.
Gradually circle farther away so that the approach is longer, and say "look" each time as soon as you face the judge. The eventual goal is to make the last turn in the gaiting pattern and to be able to say "look" and immediately have your dog look at the judge and travel straight at him. It provides a beautiful image for a judge to see on that last section of the gaiting pattern.
Of course, you have a baby still so it will be some time before these all come together - but it's fun to start them young!
Melanie and the gang in Alaska