We are building a kennel with a separate whelping room and I am trying to find a quality doggy door that we can put in the wall (not the door). The exterior is rock so it is pretty thick and I cannot find anything that will work. Being that it is going in rock it will be hard to replace so I need something they can't chew to pieces. Is there anything out there like that?

Take a look at Mason Kennel Systems.

If you frame the opening in the wall with a wood frame would that work better than than putting it directly into the rock?

Yeah, we planned on framing it with wood but it looks like some of the doggy doors are plastic and some aluminum. Are there ones that are more difficult to chew? The plastic ones look easy to chew right up but I'm afraid the aluminum ones would cut their mouth if they tried to chew it. Too many to pick from!

http://www.moorepet-petdoors.com/Wall-Mounted-Pet-Doors-s/21.htm

I have this one,, been in there for 3 years.. no damage from dogs.

We have Plexidoors in the house (wall) and the kennel runs. There is a kennel model which is heavy duty and works the best for us.
http://www.dogdoors.com/
Good luck

We use doggie doors from Gun Dog.

They have a lifetime warranty which includes chewing. If (when) the dogs finally destroy their kennel, I expect the doors to be the only things remaining.

http://www.gundoghousedoor.com/

Has anyone had any luck useing a doggy door that will let dogs in and out but keep cats in? I would like to put one in to let the dogs into the fenced back yard, but we haven't because I don't want the cats out side. Any sugestions?