Duffy has been trained to use wee wee pads. As a small puppy I would take the pads outside and when he piddled I would make sure I got some of it got on the pad. Once inside he would be interested in smelling the pad and would piddle. After a short time he was completely trained and has never missed the pad unless I forgot to put it down and then he would go where it should have been. Interestingly enough, he has never lifted his leg inside; he squats like a girlie girl but outside he lifts his manly leg.
I use the incontinent pads they sell at the drug store, far cheaper than the pads the pet store sells. It's a beautiful thing; no early morning walks or late night trips outside.
When we fly I go to the ladies room at the airport and put a pad on the floor of the stall, I go, he goes and off we go. The minute he see a pad he marks it.