Yup, Jojo is right! I am a HUGE fan of the doggy doorbell....or poochie bells. Lady uses it every day.
They are fantastic and they pick them up quickly, and you can bring them to other people's homes when visiting, so that your dog even when not in it's own surroundings, they can still tell you when they need to go outside.
Our technique was....hang the bells on a hook next to the door. when we would take her outside for the washroom, we would take her paw and ring the bells, then straight outsied....we did this for 1 day and by day 2 she was ringing it to go outside.
Lady was not good at the whole potty training thing....it took her a long time, and it was the bells that finally got us without an accident.
Let me know if you have any questions.
my bells are from a company called Poochie bells, but...you can use just a regular few bells on a ribbon or somehting