My GSD puppy is almost 4 months old and last night he started to show aggression towards my other dog, who is a pug. They play so well together and has never aggressively growled at her until yesterday, when as soon as she approached him he would try and dominate her by getting on her back and started growling. Now he has done this before but no growling was involved, I would take him off of her and then they would just start playing. However, he keeps doing this growling thing and even started growling at my sister in laws dog while he was trying to eat. He has never done that before.
Since my pug is so much smaller than him, I just don't want this to become a problem when he gets older. He is my first GSD, and he's a different ball game then my pug lol! Any tips or advice? Is it just a phase? He is a great dog besides doing this yesterday.