Bob Full said: nature is not optimal, it is just good enough.

So maybe we can exceed some nature solutions using technology.

Metal spines are an example. Hard metal is harder than any other biological spine material.

This also changes the "hard" or "penetrable" surface perspective. We should not deal about absolute but instead of relative hardness between spine and surface material.

The standard material hardness also changes when dealing with sharp indenters. A hard, but disomogenous material (like concrete or rock agglomerates!) could turn out to be not so hard when penetrated by a very sharp claw/spine.