I know exactly where you are coming from..
Selby is now 8 and we have the scars, finger, lip neck face... Really bitten, I dont know how we managed to get this far😉 Trying to put his lead on he would snap, so When I tried to put his lead on I would make it a good thing and gave him a treat,, now I do not need to treat, when brushing him I put a muzzle on, he actually loves having his muzzle on, maybe he feels safe, we have just muddled through and dont know if we did things right, but he is so loving with me but not hubby, if people come to house I have to put him in another room, its all trial and error, he is fine at the groomers and vets, i can now even give him a tablet down his throat, i think they are like children, they have to have boundries and you have to be consistent, He is my baby and I love him to bits, but he is gobby😀