Removing rear fenders and bed?

[jaredstillwell]

Hello everyone, Im new to the forum and also new to doing any type of restoring. That being said, I am having a little bit of an issue with removing my rear fenders and bed. How do I stop the bolts on the top-side from moving when I am using my (if I remember right) 9/16 wrench on the bottom side? The bolt top is solid with nothing to grab onto?

Any help would be greatly appreciated.

Thanks-J