Doors – Steel Entry Door Paint Removal

This article provides a pretty good run-down.

1. Yes you should clean: soap and water or any other mild cleaner is good.

2. You may not need additional primer, but you should fix any dents/scratches -- they will stick out after you put the new paint on. Auto-body filler (eg Bondo) works for dents and deep scratches. Before you prime, the whole door should be lightly sanded using 120-150 grit sandpaper to roughen the surface, and then wipe the whole door down to get rid of any particles from sanding.

3. Use an oil-base primer, and again, be sure to lightly sand first.

I would avoid drilling into the door for a couple of reasons. It may void any warranty on the door and if the dog was able to get a corner or edge loose they may damage the door pulling at the plastic. Cut a piece of lexan or plexiglass large enough to cover the area of potential damage. It needs to be large enough so the dog cannot grab the top while on its' hind legs. If it is a large dog you may have to cut a hole to go around the door knob. If the door has a paneled design stamped into it drill several small holes in the bottom side of the Lexan. This will prevent condensation from forming between it and the door. I would then adhere it to the door with clear exterior chaulking applied around the entire perimeter of the panel. It may help to lightly sand the Lexan where the adhesive will be to get a better bond. Position it in place with clamps or duct tape until the chaulking has set.