Can I ask what you do when Barney shows aggression? Because if he's frightened, it sounds mean, but the last thing you should be doing is consoling him and basically confirming his 'belief' that there is something he should be scared out of his wits about. You need to find a way of breaking that cycle.

I've got an oldie rescue, collie/lab x, and the best thing that works for her is just to give her space on her own if she shows aggression around the home. She's a very submissive and insecure character, its taken her a long time to come out of her shell - she's rewarded for settling down and not worrying, never for the insecure behaviour. And by reward, I mean she gets a good lass, and just enough fuss, long slow stroke down the back to keep her calm and happy.

She doesn't often show aggression with other dogs out and about, she reacts to other dogs that try and sniff her, and because she's so submissive she's a target for bullies. Basically I always try and intervene with the other dog, then she can keep herself to herself, and is quite happy with that.

Dogs don't have the same thoughts and emotions that humans do, and its a mistake to burden them with that. It took a long time to explain to someone about chewing, Tau has been a phenomenal chewer in her time, but that's what some dogs do, and if I leave stuff out she can get to then its my fault, not hers. She will sense my disappointment with her, but she won't know that she has 'done wrong', she's reacting to me. She can as much write me a note saying she's sorry for chewing my designer leather jacket, as feel 'guilt' about it, and know that it was wrong. In fact she usually quite gleefully retrieves me whatever object it is that she's chewed

Seeing a good behaviouralist will help you step back, and see things from the dog's perspective, its a good eye opener and will hopefully help you no end.