How do you get cat urine out of the carpet?

My cat has been repeatedly peeing in the same spot in my granddaughter's closet. We have been smelling it for a while but couldn't find the source, and we just figured out it was in the closet. We shampooed that area of the carpet and then put baking soda and vinegar on it, and now we have the windows open to air out the room. I did this around 9:00 this morning. Now the smell is not as strong, but still there. I have also been putting baking soda and vinegar on the carpet in hopes that it will rid the smell. Do you have any other suggestions of what I could do to get rid of the odor?