When Nebo was a pup I'd say OUTSIDE! then hurry and rush him outside. I don't believe he ever went potty in the house when I didn't catch him, as I watched him like a hawk (not just for potty, he gets into things/eats stuff too). I attached a bell to the door and rang it when I took him out. He caught on really fast, now he rings the bell when he wants out...which is great, because Nebo rarely barks, so it's a good way for him to let me know.
Smokey has to wear a diaper, he pees in the house ALL the time....sometimes I yell no but usually I don't even bother, he won't stop.
Reggie is older too, and has had a few accidents...though all the recent ones, nobody has caught him in the act.