Plan C utilizes plan B's Plexiglas, but also includes the use of mono-line which is stretched across the face of the nest box. The mono-line prevents a woodpecker from clinging to the box's face, but doesn't inhibit other desirable species from entering and exiting the box.

The mono-line is that which can be used to hang heavy picture frames--70 pound line in this case. (Woodpeckers will break 10 pound mono-line.)

Did it Plan C work?