Professional groomer here. Please don't tie him up or muzzle him. Bite the bullet and take him to the vet to be knocked out and shaved down completely. Then start from scratch as you should have when he was a puppy. Start by pairing the brush with something he loves. It can be a food treat that is super yummy, talking meat or fish or cheese, not milk bones or Charlie bears.Or, if he is a ball fanatic, you can throw the ball for him. Start with a new and different looking brush, show him the brush and give a treat, while hiding the brush behind your back.Show the brush, give a treat (or throw the ball) repeatedly for 10 mins or so 2 to 3 times a day, every day, until he sees the brush and looks happy and anticipating his treat. Then, and ONLY then, touch lightly with the brush, on an area of the body that is not super sensitive, such as his back, then treat as before, touch and treat repeatedly several times a day, etc. Then graduate to lightly brushing, always pairing the brush and brushing with something positive. If he gets tangled, cut it out, rather than pull and hurt him. Handle all parts of his body every day, pairing with a treat, separately from brush training. Feet, tail (if he has a stub, handle that) muzzle, ears, etc. You will want to cut back on regular meals so he doesn't get fat, and is still eager for the treats. In the future, after he is better accustomed to handling, you may want to get him shaved down a couple of times a year to keep brushing easy. It's your job to train him to allow handling and grooming, with out having to manhandle him. Think about how scary it can be to be tied up and muzzled, and have people do scary things to you when you don't know why. Brushing tangles hurts, and only make them hate the process more.