How do you keep plastic leveling blocks from slipping?

Allworth wrote:
I keep the "Leggos" from slipping by using pieces of 2x8, 15" long with a bevel on each end. One in front of the front tire and one between the tires. Pull forward.

Thats the way. Planks of wood are cheap, useful for things other than leveling, good for helping to get one out of slippery situations on grass, as a standing platform across the bed of the truck for cleaning the front cap, when they finally split good for a nice fire.