Hi,
I started Kacee out on door bells as just a baby. They catch on to them in absolutely no time at all. Kacee is now nearly 16 months old and never, ever has accidents!
Oh! I wanted to add that sometimes she hits it with her paw, too, and sometimes just uses her nose. Once in awhile she'll bark as well or make some weird crying noise along with ringing the bell. I love those bells! I can hear them all over the house!