We have a sliding glass door without a pet door. I woke up one night to a skunk pushing on the patio door, apparently looking for the pet door (and dog or cat food) entrance. Our neighbor has trouble with racoons getting into the cat food.
I think if we got a pet door it would have to be one with a microchip to keep out all the critters we have in our area. I saw this on youtube but I don't own one:
Even clouds seem bright and breezy, 'Cause the livin' is free and easy, See the rat race in a new way, Like you're wakin' up to a new day (Dr. Tarr and Professor Fether lyrics, Alan Parsons Project, based on an EA Poe story)