Great advice.

I too have a rottie, but now he's 12 years old. We never did have much trouble with him doing that but my moms rottie sounded similar to yours. He always was growling trying to show he's the boss.

When he did this behavior my mom would stop, and say "NO" in a very stern voice then ignore him for a minute or so. Each time he did it she would do the same thing. It didn't take him long to realize he hated being ignored

Hope you'll share more stories and pictures about your little cutie pie Cain!