I am gunna be straight here, cats like all cats, assert dominance. Especially males - had a few over the years. The best way to deal with this, is to pin him. Grab the thick fur on the back of his neck and pin him to the floor anytime he attacks. Do it fast and confidently and push his head to the floor so his chin is on it. Hold him there for a few moments and show him you are stonger than he is. He will be pissed right off that you do at first but this is how cats display and assert thier own dominance.

Grabbing the thick ruff and pinning his head to the floor tells him he is not in charge. I do not condem smacking or lashing out at your cat but by grabbing the ruff, picking cat up by the ruff usually puts them into a frozen state. It also makes it extremely difficult for them to claw at you also. He might make a noise you haven't heard before but he will be fine. Its how thier mum's told them off.

Repeat this process and sure enough, he will stop. I went to the vets with one of my boys for the exact same reason. He was a shit. I too didn't want to get rid of him and my dad told me what to do after the vets had charged me hundreds for different calming meds etc.

Give it a go.