When Riley was a pup, we decided that we wanted to try to train him to ring a bell on the door when he wanted to go potty. Every time it was time to go potty, we would take him to the door and ask him if he wanted to go potty and to ring the bell. We would not open the door until he ran the bell. He was very easy to train.
The trick to this is to only get him to ring the bell to go potty, not to go outside and play. Riley has mastered this. Travis is a slacker, he lets Riley do it for him.
People never believe me when I tell them that Riley rings a bell to go potty, so I video taped him. This also is proof, that if Riley was human, he would be a cheerleader. He does EVERYTHING with such enthusiasm.