So far, I see the Add A Motor, the Chicken Door, and the...heck, I forgot the third one. My question is this: what keeps the door closed tightly. The Add A Motor one looks like the door just goes up and down on a string with no plan for keeping the door rigid to keep out varmints. If that is so, what's to prevent a coon or possum from raising the door. The one that does seem to have a tight closing design is the Chicken Door one for $180.00. Help me out here. Is this what I'm seeing?