This may sound like a silly suggestion - but has nobody (manufacturers) ever considered putting some sort of mesh grill over engine intakes?
Surely if the mesh was of the right gap size there would be little
performance impact. It might even save a few engines from bird strike damage as an extra benefit.
If Braun/Phillips/Remmington can make a hair-dryer efficient and safe by putting a grill over the intake i'm sure CFM/RR/P&W could do the same on a larger scale!
G.