Here's a situation for you.
I want to haul pallets in a dump trailer with only a single D ring in the front center of the bed. 2' side walls. Stake pockets at the top of the sidewalls. The pallets are about 4'x4' and the dump bed is about 7' wide. I can't figure out how to immobilize them. Do I need to if I limit the height of the material on the pallets to 2'? I'm sure that for most trips it would work, but I worry about that one trip that doesn't go as planned. I figure if I plan for the worst case then I won't have any problems.
While on the road, I've seen that situation where the top pallet was placed on edge and the straps run over it to the bed sides.
For more stability, the top two pallets could be placed in an inverted V, as seen in fields.
Bruce