House Training Prob - with a difference

I am (or thought I was) an experienced dog owner but my new puppy is proving difficult (or maybe its the owners). He is now almost 16 weeks old which I know is very young and wont 'go' when we take him out on walks. He will go in the back garden after the walk. Also sometimes we put him in the garden and he wont do anything but then comes back into the house and performs. Any ideas????

what do u do when u bring him in and he "goes"?
   
when u see him going inside correct him with ur voice and put him right back outside and don't bring him in until he goes. when he does go outside praise him. he'll then see going outside is a good thing.

btw, he's a gorgeous puppy!