My babies are also pad trained and I make sure that one edge of the pad is against a wall so that I can lean the edge of the pad up against it. Both of my boys know to lift their leg against the wall.
I've also heard of people making a pee post - they fill a liter bottle with water to weigh it down and wrap it with a pee pad and set it in the middle of the pad on the floor.
__________________  Eva and her keikis: Hokule'a, Kalani & Pi'ilani |