Aggressive Adolescent BC

Update for anyone who has the same problem and has come across this post - stick in there! We followed the advice in the comments and its only been a couple of months and he seems to be back to his old self again! Potentially the adolescent phase as well and hormones kicking in. He's 14 months now and seems a lot happier and more relaxed.

My 1 year old BC is aggressive towards me and my partner or anyone who tries to make him do something he doesnt like / groom him / vets. It all started with a vet visit when he was about 7 months (pinned down, muzzled) and he's had opportunities now to reherse this behaviour over and over to the point that he will give you a very scary warning and a bite. He has bitten us a few times.

Posting for morale support really, I keep coming so close to giving up on him. Any time we make progress, we have a set back not long after.

We saw a trainer last week who had suggested ecollar and talked us through how to use them, however when he left we couldn't get the collar on him without getting bitten. We had some success at the start with rewarding recall at a level 1 / 100. We are struggling to make progress with muzzle training for the same reason, as soon as we get a strap on he goes on full attack and then its days of him being suspicious of us.

In terms of his other training, he knows every command, every trick, he loves to learn! And when he's not in this mindset he's great. He's so charming to strangers in the street! What a good boy, so lovely, and I am smiling but it makes me so sad because I know the truth.

He won't go into boarding kennels as it reminds him of his vet visit and I am too scared to have anyone watch him in the house because he has turned on family members / visitors in the past. I want to get him neutered but we can't take him to the vet because of the same reason. He uses this aggressive response to get out of any situation that displeases him.

The plan is to really focus on muzzle training as a first step until we work on anything else. Has anyone had success with this with a really suspicious dog? Has anyone had success with a dog like this? Did neutering help??

Sorry for the long post, I just feel so alone in this.