There are many different types of dog doors out there. The cheap ones don't last very long, but if you can get replacement flaps it will help. I just recently bought a new one. It's called a Multi-Flex Pet door. It seems to works quite well and hasn't been blowing open by the wind, which was the problem with previous door. The door I really wanted was the Plexidor, but it was just too expensive.
I would buy the best door that you can afford. It will probably be worth it in the long run.
