Great Dane Potty Training?

I am having a little trouble with Thor. He is an 9 weeks old great dane, and I have had him 3 weeks.
We take him outside quite a bit, at least every two hours when we are home, when we are not home and at night, he stays in his crate.
We praise him like crazy and give him a treat every time he does his business outside. And he never messes in his crate.
He does pretty well with number 1 but it is number 2 that is a problem. For some reason he will not poop outside. No matter how often we take him out, he will pee outside, and then 5 minutes later poop inside. When I see him, I will say "No!" sharply and take him outside right away, and he will still not poop outside, he will hold it until he is inside and I am not looking.
I am out of ideas. I know he is a baby, and it is not his fault. And I know I need to be patient, but I need to see some sort of movement in the right direction so I can use positive reinforcement.
Answers:
Start potty training over.don't lose sight of the the puppy...
Whenever the dog is in the house and not crated put a body harness and leash on the dog, tie end of leash to your belt. Wherever you go the dog goes. When you see the dog start to signal (sniff/circle/scratch) that it's got to go than run the dog out to where you want it to go. Praise, reward (immediately) and use a command word consistently. When the dog shows it's learned to go outside consistently by dragging you to the outside than you can undo the leash from your belt. Keep the leash on the dog still and keep an eye on it whenever it is in the house and not crated so if it starts to make an accident you can grab the leash and run it outside. Once it is going outside with no attempted accidents for at least a week than you can take the leash off.
The most common mistake in potty training is giving the dog freedom to roam the house without supervision where the human doesn't see the dog signal it needs to go.
Also, if he won't poop (and you know he should be) when outside than walk him back inside and to his crate. Keep him in ther for five minutes than back outside, keep doing this until he does poop.

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take her out when you get take then out after they eat and ever couple hours

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It's only nine weeks old. It could take up to another 6 weeks before he gets it.
I have a Newfoundland (another big dog). It took awhile to get him to go always outside (about 15 weeks old) My advice is to stay with him outside for up to a half hour at a time, until he finally goes poop outside. Then go over the top in praise. He'll get the idea that he has to go outside.