I have recently rescued two malamutes (4 & 1yr old) that I'm trying to teach them how to use a doggie door. They're very skittish and shy, but we've made significant headway in building trust and allowing them to get comfortable in their environment. We've been exposing them to the door by holding the flaps open and they go in and out, but they show no interest in pushing the flaps in order to walk through. Any suggestions for how to teach them to push on the flaps??