Housetraining problems...?

We brought home a lab puppy about half a week ago. He is seven and a half weeks old now. My husband and I are trying very hard to housebreak him, so he doesn't ruin our carpeting. We watch the puppy like a hawk and bring him outside after he eats, naps, plays, etc. When he does go outside, we praise him. When we catch him in the act of urinating inside, we quickly rush him outside, but he just stops going...and won't finish going outside. Any suggestions?