How do I prevent my patient from sliding down the stretcher when the head section is raised?

How do I prevent my patient from sliding down the stretcher when the head section is raised?
 

To help prevent your patient from sliding down the foot end of the stretcher, Hill-Rom offers an exclusive Auto Contour™ feature that automatically raises the knee section when the head section is raised. When activated, the BackSaver Fowler® mechanism built into the Auto Contour™ feature will drop the seat and automatically raise the knees to prevent your patient from sliding forward. To raise the knees even further, the knee gatch option is available.