If you want your tombstone to survive a long time as a legible monument to your greatness,

Question:

If you want your tombstone to survive a long time as a legible monument to your greatness, should you request that it be made of marble (a metamorphic rock consisting of calcite), or slate (a metamorphic rock consisting largely of fine-grained muscovite and quartz), or steel? (Request burial in a temperate climate)