What kind of damage have you experienced, that you are trying to prevent? I have seen SPAD combat planes drilled into the ground at full throttle, and the wings have looked good as new.

I think that filling the wing with foam will make it fly more like a brick than they already do.

I like the idea of a music wire spar, like in the GNAT and SPA3D plans, it stiffens up the wing pretty well. Maybe you could so something similar on the leading edge.