Why does my dog pee on my furniture?

There are so many reasons a dog would urinate on your furniture, a male marking, a dog not fully potty trained, a dog becoming incontinent. Much more information is needed to properly answer your question.

-Sex of the dog -Age of the dog -Level of potty training -When does he pee? -Exactly where does he pee?

I agree with the answers given. Until more information is known, some solutions are: - to use a diaper (reusable or disposable for both genders) or belly band (if for a male dog) - secure the dog to a limited area that can be easily cleaned when not observed (maybe a crate or playpen) - tether the dog to you with a leash while you are home - so wherever you go, the dog goes - so you can instantly stop unwanted behavior as needed and also gain more insight as to when & why it's happening.