i think you all should use a bell.
i trained cody on the bell, and whenever (even 3 floors up in an apartment), he has to go out, he rings the bell and sits by his leash. he's my angel.
it was annoying for a while though. he abused the bell system. he would ring the bell, run half way out of the garage and then fly back in a sit by the "cookie" jar. he would do that about 15 times in 10 minutes. ...he is too smart for his own good!
but anyway...the bell system works SO well, and then there is no guessing....yo u hear the bell, and take them out.
its been harder since i got angus, i'll be in my room and hear the bell, and he will be chewing the damn thing in the living room. SO....its not for every dog, at least not the "special" ones. lol