What could it be?
I'd like to start off by saying; I own my very first dog in my life and it is an all black GSD, Hugo. It is the best decision I have ever made. He is incredibly smart, loyal, and social. I got him down at school and trained him every day. Recently, I have graduated and moved back home. Upon meeting my dad, Hugo spent the whole day playing in the water and eating scraps of human food. One of my major rules was ABSOLUTELY no human food, but my dad still does it from time to time. (I yell at him every time) Because of this, Hugo is absolutely obsessed with my dad. It's great that they get along so well.
Having said all of this, Hugo used to hang on every one of my words and obey me so well. Since he has been hanging out with my dad, he has started to disobey me what seems like deliberately. Also, my dad lets him roam around outside unattended at our cottage in the country. Since this happened, I have noticed that he has been pulling on the leash and disobeying my heel command. He has never done this before. He is only 8 months old. I was wondering if this is just his stubborn stage or is my dad being a bad influence on my dog? Please help.