If the matting on your dog is severe, the safest and most humane way to remove the mats would be to clip their hair short. The length of his hair will depend on how tight the mats are. A groomer must be able to get the blade under the mat right against the skin to remove them. If the mats aren’t too tight, sometimes the groomer can get longer blades underneath the mats to salvage some length. However, if the mats are tight to the skin, the groomer would need to use the shortest blade available to remove the mats. This would result in very short hair but would give you a fresh start and make your dog much more comfortable.