My post is going to make me sound like a bad dog owner... so many instances of Kobe doing something bad
Anyway, I thought more examples would make the situation clearer:
1. In response to Connie, it doesn't seem like leash reactivity. He has been in an off leash park before and was perfectly fine with small dogs, but tried to rush at and attack larger dogs who came in after. That's usually when we put the leash on and take him away, but it's not the leash that got him that way in the first place
2. We thought he might be being territorial, and that may be true to some extent. e.g. he will *bark bark bark* when guests come into the house, and generally get very stressed, but when we leave him with our friends when we go on vacation, he has no problem with their guests.
3. He feels threatened in *HIS* house when people come over. He's usually alright when they are sitting down. He doesn't like it when they get up and walk around.
4. We haven't tried leaving him alone with anyone, but when we go on vacation and our friends walk him, he has tried to lunge at passers by/joggers who come too close to him
Not discounting all the other responses, but Moemer's suggestion sounds like it might be correct. It might really just be a confidence thing (since we already do know that lack of confidence/ fear is a major issue for Kobe). We've noticed that when Natsu is around, he is much worse than if we take him out by himself! I can see him being territorial or possessive as well too...
Great suggestion on the spring loaded gate!!! going to bug the husband to put a spring on ASAP!