Staplelok fenceposts are a high-tensile, galvanised steel section, with a scalloped groove down one side of the post. The staples that hold the wires to the fence are banged into the groove with an ordinary hammer and lock into place. They will not slide or come out until removed with the Staplelok staple remover.
In fact it would take between 300 and 400 kilograms of force to pull the staple out without the staple remover. The posts are extremely strong and very light (2.2kg) compared to fence posts - a farmer can carry up to twenty at one time. Remember even Colin Meads could only be expected to carry one or two wooden fence posts.