well my other dogs used to bark at the door and as soon as they barked and gone to the toilet they used to get a treat. thats how we taught it.
bella wont we had the same problem as you but shes realised that she needs to ask to go out or she wont get her treat so she jumps up and trys to hit the handle now. not as handy as a bark but it will do.
We did think about buying something she could press and it would ring but she started tapping the door fortunalty
Main training aid . dog chocolate:D armed with that and you should get the job done. bella now knows the names sweets and chocloate
easy to recall her with them too
Shes funny like that she seems to know what chicken and ham means too and frolics . and if you even mention the word out in a convo shes at the door before you know it
there not as stupid as they make out