Protect the wall from what? The root system? The pine needles?
The WRC has a shallow root system. So, depending on how deep your wall goes AND how 'shallow' the roots are, I don't know if you have to worry about the roots possibly undermining the wall. (This is problem #1 ...)
As for the roots being able to 'grab' onto the wall, itself (underground), again, I don't know the answer but this is problem #2.
If I'm way off, maybe you need to say more about what's going on w/your project. (It can only help us to help you.)