I have a 7 month old intact male Border Collie. I got him when he was ~4 months. I live with three other roommates and close to my family. When I first got him, he was timid around people and would spend most of his day in the basement instead of out and about.
It seems that his timidity has transitioned to aggression, he now barks and growls at my roommates whenever I am not home. He does the same when I visit my parents and leave briefly. When I am home, he barks at my roommates but ignores my parents when I visit.
I tried to remedy this issue by having them provide him with treats and make him do things he understands (ie, telling him to sit and rewarding him). This worked for a little bit and he didn't bark at the roommate that I did this process with when I was home.
One of my roommates (understandably) feels uncomfortable around the puppy since he's acting so aggressively and would prefer that I keep him in the basement when I am away. Naturally, I would like to avoid this outcome. Especially since two of the roommates will be leaving at the end of the lease and I will need to find new ones.
What can I do to alleviate my dogs anxiety/aggression towards other people while I am gone? I have him crate trained, but I don't think it's fair to keep him crated up when I am away for 8+ hours each day during the workweek.
I don't know if it's relevant, but he seems to be just fine around my sister even when I'm not around.
I sincerely appreciate your help, thank you.
EDIT: As of the time of this edit, he has become significantly better. I think the reason is at least partly because I moved out of the house. He may have had a poor experience with one of the roommates while I was not home which caused him to be anxious and stressed. Now that I live in my own home, he has calmed down quite a bit. Even in public and with strange people / dogs, he's doing so much better. Granted he's still nervous. But he is no longer aggressive or (too) fearful. He was also neutered and is older now which probably played a big part in calming him down.
Some additional measures I took to ensure his success were feeding him exclusively through puzzle toys and something called a "Foobler" which keeps him occupied when I am not present.
As to what combination of these things is responsible for him calming down so much, I am unsure. But I do feel strongly that removing him from that house played a big part in that.