Are you talking about uld's shifting on full flights or partly loaded a/c, as this makes a difference. On a 747 in the lowerdeck, for some combinations of containers you will need a required nimber of uld's, to fill up "zoneloads", to prevent containers to shift in flight.
as an example, if you load an ld1/ld3 on position 11r, it is mandatory to fill up as well 12r. On the other hand 13l /and 13r can be locked individually.
