I train puppies to ring a bell hung from the door leading outside. It only takes a week or so... granted, you have to let them out when they ring the bell to play, too. But once they get in the habit of pottying outside, they are fine (but maybe my ease-in-housebreaking is abetted by having older dogs who "show the way")
Best dog moment ever: 9-week old Jimmy had just tinkled on the floor, and Ike walked over, took a sniff - and then I swear he said "DUDE! We don't do that in the house!" Jimmy never pottied in the house again - until 10 years later; and that's how I knew he had developed diabetes....