i tried to bell train princess and she seemed to get the hang of it but she would be confused if someone came or went out the door and she would sometime ring it when she didn't have to go or when she was yelling at the pug & owners she despises across the hall.....
...anyways, i just began letting her "tell" me she has to go out. she will give me a total death stare, lol, and if i don't look at her she will bark. before i can get the 1st sound out to ask her she darts for the door and starts bouncing off the wall & leash hanging there...yes, she's a spaz!
and now that she's older (about 13 months) she asks to go out considerably less than she used to. puppyhood is so hard, but it pays off once they do mature.
good luck.