Okay, I trained Riley, the cocker, to go to the door and hit the jingle bell whenever he wanted to go out. The bell isn't always on the door so Riley trained me to let him out when he stood at the door, looked at the door, and barked. (I think he went to barking out of frustration because he couldn't get my attention when I was lost writing on the computer.)
Riley now moves his food bowl around the floor and will eventually couple that action with a bark if I'm too slow and when he's thirsty he will sling the water dish around and eventually bark if I don't move fast enough. He's managed to put together the fact that a visible action with noise coupled with a bark gets me every time.
The food dish is heavy and he will knock it against the cabinets. The water bowl has a different sound when it's slid across the floor.
I actually don't mind it because I do get very preoccupied. When Riley has to go, Freddie the Maltese is ready and willing. So I get 2 for 1. My Shih Tsu will quietly use his potty pad if necessary or wait and go with the others.
Dogs are smart. They may not stop with what you teach them.