How can I stop a Maine Coon from scratching the sofa?

First, you need to figure out what exactly your cat is scratching-the material, the location, and the texture-because that determines the fix. For a Maine Coon, they often scratch to mark territory and stretch their muscles, so simply yelling or removing the sofa isn't enough. I'd recommend getting a tall, sturdy scratching post made of sisal or carpet, placed right next to the sofa's corner they target, and cover the sofa's arm or edge with a double-sided sticky tape or a clear vinyl shield for a few weeks. Once they consistently use the post, you can gradually remove the tape. Also, make sure they have enough vertical space like cat trees or shelves, since Maine Coons love climbing and need an outlet for that energy.

Put a scratching post right next to the sofa corner they target. I've had luck covering that spot with a clear plastic carpet runner upside down-the nubs feel terrible on their claws, so they lose interest fast. Maine Coons are big cats that need a tall, sturdy post, at least three feet high, or they'll just go back to the couch for a proper stretch.

A scratching post is only half the battle, you also need to make the sofa less appealing. Try spraying the area with a citrus-based deterrent or placing double-sided tape on the spots they target, cats hate sticky textures on their paws. For a Maine Coon, I've found that offering a horizontal cardboard scratcher near their favorite napping spot works wonders because they love to stretch out flat while scratching, not just upright.