[cos]

Sedation is an option, is personally rather just shave him bald myself and start over though. If he's badly matted, as has already been stated - he could be in pain.

Shaving in a calm environment by someone who he trusts without having to be put under GA would be the best option in my opinion. Unless he shows fear or stress towards you - in which case id go with veterinary grooming under sedation

 

[cos]

If he's matted behind the ears or legs those are really sensitive areas and are probably causing some amount of pain, and a dog in pain may lash out no matter how much they trust the person, especially if they're already nervous, so be careful!

I'd just buy a dog clipper. You can find them at a lot of pet stores that offer grooming like petco or pet smart