Big Potty Accident

Rex had made it 6 days without any accidents in the house after I got to the point I would put him in his crate everytime he had an accident. Well, I was just sitting on the couch and he squatted and peed.
How do you punish something like this? I gave a good firm "no" and put him in his crate. We are going to be gone most of the day tomorrow and I didnt want to leave him in the crate for possible 8 hours, but now I don't think I have a choice. Help!!!!