Before you try to shave him down, have you tried combing conditioner through his coat? If the mats are close to the skin, shaving can be tough too. One thing to always prevent future mats from forming, always comb or brush using a leave in conditioner. Never comb the hair "dry". I think of it as baby fine hair. You would never comb a babies hair without using a detangler or a really super soft brush. I think the same is true for a malt's hair. JMM probably has some really good adivce on how to handle a matted coat.