My dog Zelda has always been an inside dog, even when we let her outside she rushes back in when she's bored. But obviously she would need to go outside every-now and then. Typically we'd always open up the door to the back porch to let her out. She was not a dog that liked to wait, so she noticed when the old door could be pushed open with some force. So she'd run up to it and push it as hard she could with her paws, and run inside. We were able to deter her from doing it by pulling a kitchen drawer to block the door. A week or two later, she stopped trying to open the door herself.