He looks so guilty in that picture! IMHO you'll never get rid of that smell... Let's see what everyone else thinks.

Well, he looks like he's sorry.

No being a dog lover and having respect and affection for those of you who are - I think I must refrain from commenting too much on this situation.
I will say that I think NOT washing the entire bolt is a big mistake. You don't know how long this urine has been in the fabric and I have to believe that the smell has seeped throughout the bolt over time.
Suggest washing it all and using baking soda based detergent, at least once.