4-Oxo-4,5-dihydro-3H-pyrrolo3,2-d pyrimidine-7-carboxylic acid methyl ester and process for preparing are provided. Although a denser material is used for the protective cover, recesses are formed in thicker portions at impact points that create compressible ribs. The apparatus is positioned such that it is perpendicular to the direction in which the wind is blowing.