Doors and Windows - dog proof door?

I need to replace the back entry door to our 30 year old house. The old door is wood with a window in the upper section. The window slids up and down but is now warped--lots of fresh air coming in. I have 8 dogs who go in and out of the house via this entry. They scratched up the old door and I was not planning on replacing the door until spring. We are moving to a new house and will be remodeling this one for sale. However, with winter coming on, the breeze through that window is a problem. I don't really want to use plastic window covering and it is not cost effective to replace the window. I want to put in a door that can stand up to the dogs' scratching. Steel is out, wood is not a great choice, vinyl is out--a friend suggested "storm proof " glass door--he said it is pretty much impact resistant and could probably handle the scratching better than other materials. I hate to put too much money in this if I am going to have to replace it again in the spring. I have thought about a pet door but only found some that were aluminum storm doors rather than solid entry doors. Any suggestions?

If you want a quick, temporary fix, I'd get a piece of acrylic from your local home center and cut it to fit over the door. Attach it with something that can be removed easily - 3M command adhesive comes to mind - and then take it off to show the house or when you move.