In nature, there are three positions in the dog pack ' front, middle, and back ' and each dog will gravitate to its natural place based on relative dominance, with the pack leaders always in front.
Each position has its own function within the pack as they work together to survive. The dogs in front provide direction and protection to the pack. They determine where the entire pack will go, and they fend off any dangers from the front.
The dogs in the rear are primarily concerned with alerting to danger approaching from behind, and their function is to warn the rest of the pack. The dogs in the middle are mediators, communicating between the rear and the front.
Every function is important. Without the dogs in the front, the dogs at the rear don't know where they're going. Without the dogs in the back, the dogs up front are not aware of any problems coming up from behind. And without the dogs in the middle to relay messages, the front and back of the pack are isolated from each other.
In a human-and-dog pack, every human should always be at the front of the pack, as the leaders, ahead of all of the dogs. We do this by providing protection (calm assertive energy, food, and shelter) and direction (rules, boundaries, and limitations.)
If you have a middle-of-the pack dog, she will respond well to direction, while a back-of-the-pack dog will respond to the protection.
A front-of-the-pack dog will respond best to your very calm and assertive leadership.
If you have more than one dog, you have to let them figure out the pack order amongst themselves. It can be tempting, when we bring a new dog into the pack, to try to put them in a lower place than the existing dogs.
This is natural to humans because we generally give our older children more privileges and responsibilities than the younger ones.
However, it's completely unnatural to a dog. If you try to treat that back-of-the-pack dog as having a higher position than a middle-of-the-pack dog, you can create anxiety and instability in the dog with a lower position and aggression in the dog with a higher position.
Remember: work with Mother Nature, not against her. A dog's position in the pack is hardwired into him. Don't try to change it, because you can't.