I have found a way to protect your heads by using trapdoors. By locking a trapdoor that is placed next to a head on a wall the trapdoor's lock will protect the head depending on the direction the wall is facing. The following will tell what side of a trapdoor will lock a head dependent on the direction a player is facing the wall.

When a player is facing
NORTH/SOUTH:
Left/Right of Trapdoor will not lock a head


EAST:
Left of Trapdoor will not lock a head
Right of Trapdoor will lock a head


WEST:
Left/Right of Trapdoor will lock a head

 

I remember while doing some LWC reports that trapdoors would sometimes lock more than just the block that they are attached to so I did some testing ;)