What is it going to take before you listen to people who have advised you time and time again to never allow any Parrot onto your shoulder who is know to bite. This is never a good idea. you are really going to get hurt and the one who is going to pay for this is the Macaw. This is really not fair for both of you. You really need to reach out to someone local in your area who can work with both of you who knows what they are doing and how to handle a Macaw who bites. Shaking a Macaw while they are biting only makes the Macaw bite more, the tip here is not to pull away or shake but press whatever part of your body is in the beak to the back of their throat. they will release you. The reason being, one they are now off balance, they gag on the part of the body and will do whatever it takes to get away.
There are so many tips on how to handle this type of behavior and it's very easy to learn, you just need the right person to guid you but you have to listen on what people here are telling you. So i will say this one more time, DO NOT ALLOW THIS BIRD ONTO YOUR SHOULDER. Perhaps making a video of your Macaw can shed some light on his behavior as we who have Macaws can give better advise to you and what to look out for to prevent bites. Best of luck Joe