My mom let’s her big dog stay on the couch. I decided to teach her a true lesson

The dog always has a spot on the couch when I visit my mom. He acts like he owns the place. Some people might not think much of it, but for me, it’s a big bother. I’ve been letting it bother me for years. Since I have a young daughter and have been diagnosed with OCD, sitting on a couch where a dog has been is not only painful, it’s unbearable. Still, my mom doesn’t seem at all upset.