My Chihuahua puppy is almost six months old. House breaking has been going pretty well until this week when he discovered how to lift his leg to urinate. Now he is going in the house instead of outside. I have confined him to the kitchen and he goes out every hour. I caught him in the act a few minutes ago, I grabbed the scruff of his neck and, "NO!" and immediately took him outside. Can anyone please tell me what I am doing wrong?

This is not a matter of housebreaking, but status. Having a good pack structure reduces such problems. The dogs see all the
People and dogs in the household as a pack with each having their own rank in
The pack and a top dog. Life is much easier if the 2 legged pack members
Outrank the 4 legged ones. You can learn to play the role of top dog by
Reading some books or going to a good obedience class. A good obedience class
Or book is about you being top dog, not about rewarding standard commands with
A treat. Start at http://www.dogsbestfriend.com/. Too many people fail to obedience train small dogs. They end up with the marking you have and other problems. Have him neutered.

Catching him in the act of marking calls for stronger corrections than the
Otherwise effective "Bad dog!". When it misbehaves, throw it on its back, and
Growl "Bad dog!" right in its face. Hold it down until it lifts one back leg
To show submission. You can pick him up with your hands behind his front
Shoulders and hold him up with his back to you. Keeping him far enough away
To keep his head from smashing into your face, hold him until he stops
Struggling and relaxes. Others like the squirt bottle. Fill it with water
And a little vinegar or lemon juice. Give it a squirt in the face as soon as
It misbehaves. Dogs hate that.

Thank you very much! I will give your suggestions at try, I guess we need to embrace the whole pack mentality thing. I'll let you know how it goes. Have a wonderful holiday!