You can try removing the couch in question or covering the part he sleeps on with books or other items. With no couch to go on, you may be able to see signs he has to go potty. Take him out at the slightest signs. Also, aim on training him to go potty on command so that you'll help eliminate the need to pee or poop in the evening. Make sure to clean all traces of accidents with an enzyme-based cleaner. Make sure you always have a clear view of your dog (remove bulky items that do not allow you to see your dog clearly).