Don’t use scissors! Most mats are super close to the skin and it’s very easy to cut your dog, especially working so close to his head where he can move quickly and stab himself! If you absolutely must cut it, a good set of clippers are the way to go, working them gently at skin level under the mat to remove everything without cutting the dog.
For working on the mat, keep it dry, and hold close to the base to keep it from pulling while you detangle it. It’s going to take a long time, but you should be able to tease quite a bit out with your fingers.
I don’t know what breed of dog you have, but if he’s double coated you might consider an undercoat rake in addition to his regular brushing. Those things work wonders on my dogs, and don’t pull or break the hairs like some of the marketed “de shedding” tools.
