This works very well for urine spots and stains. My neighbor's son is in the middle of potty training, and his first night sleeping without a pull up didn't go well for him. His mother was afraid they would have to throw out the mattress. I told her to try this remedy and she said it worked wonders on her son's mattress.

Moisten the urine spot/stain with warm water, then scrub borax all over the spot/stain.

Let it dry and vacuum the area, then take a scrub brush with stiff bristles and brush the area.

Depending how bad the spot/stain is, it may take a few times, but it will eliminate the spot/stain and any odor.