Are you talikng about the tube type that flips over and is secured by two straps on the tailgate? If so the only way to secure it that I know of is to lock your tailgate while you are in transport. If the tailgate is down put the clips in the tailgate latches and they snap in place. To unlock simply pull up on the tailgate handle. I don't know if you can lock while the tailgate is down or not.
Lock/ Towards the left Unlock/ Towards the right or vice versa.
Hope this helped.