They're secret missile silos armed with Yuppi and DINK destructors.
Raccoon proof...don't know. Birds haven't built a nest in it for two years. Might be they know squirrels can hop up and eat their eggs. Haven't figured that out. Maybe too hot?
I would have liked to use the bark idea but tough to find and what I did find was wet and nasty. I went with the roofing material over treated solid wood.