De-matting your dog's coat takes time and patience. He didn't develop the tangles overnight, and it is unlikely you will be able to get them all out in one grooming session. Mat removal can be painful for your dog -- the knots are tight and can pull at the skin. Break the mat removal process up into multiple 15-minute sessions over several days to keep both you and your dog in a good mood.
Spray your dog with a detangling conditioner. These sprays don't require you to rinse them out, and they soften the coat and make the hairs a little slippery, which makes it easier to remove the mat.
Work through his coat with a metal comb. You can remove smaller tangles with the metal comb, working from the bottom of the tangle toward your dog's skin. Skip over the larger mats that you know require more attention.
Use your fingers to separate each mat. Start at the sides of a mat and work toward the center. Pull as much of the mat loose with your fingers as possible. You can also use several teeth on the edge of the metal comb to help loosen the mat.
Remove stubborn mats with a mat splitter. Once you have gotten as much of the mat out as possible, use a mat splitter to break the remainder of the mat apart. Use the mat splitter to cut into the mat, working away from your dog's skin. It may take several passes with the splitter to loosen the mat up enough to get it out. Use your fingers to pull out the loose hairs once you break the mat apart.
Repeat the process until your dog is mat-free.
Brush your dog with a slicker brush, making sure you get down to the skin, where smaller tangles and knots form. Once the slicker passes through his coat, you know he is mat-free.