I have a one year old German shepherd Rottweiler mix who has just recently shown some changes in his behavior. Before we moved he was a friendly dog and he didn't have any issue with other people or dogs coming into our home. Well we suddenly had to move and I'm living back at home with my parents and their 4 other dogs which he has been around before with no issues. Well ever since one of my parents dogs started a fight with him (probably about 4 times she has started it with barking and growling and teeth showing) a few months ago he behavior has changed. He has become a bit more aggressive with new toys and treats and has started two fights where he bit two of my parents dogs (the one that started the fight before and the one that looks just like her) over a toy. This is very unusual behavior for him. I thought things might have been getting better because there has been anymore fights between them but just recently he has nipped at one of my brothers friend and actually bit another one (both times while I was not home) Now since I wasn't home when these happened so I don't know why or how these happened. I know that he's always nervous when my brothers friends come over and I don't know if thats what caused it. He is very protective and he does get anxious when I'm not around. I don't know where this behavior has come from and I'm not sure what to do. I don't want him to have be in a cage all day while I'm not there but I don't need him hurting my brothers friends. Any advice would be helpful. I. have contacted a trainer and waiting to hear back but I just thought I'd get some opinions.