What are the best material options for protecting sensors from a drill bit?

[fitz_calc]

I need a 5"x2"x1/8" 'cover' to protect some sensors from a drill bit. Occasionally the bit will run into the cover and chip away at material, etc.

I need the cover to be dull and black, coating with a surface treatment won't work because over time the coating will chip away. What are my options? Cover can be Al or Steel, cheaper is better, thanks for the help everyone!

 

[dbmorpher]

Some tungsten carbide would work good but be hard to mold