painting on a Memorial Rock

My friend that I painted the Fireplace Mantle for, asked me to paint on a very large Memorial Rock that was for her father. I used the image of the Dove and Hands that where on the Sympathy card I had sent...this because they liked it so much. After a couple of years the image pealed off because the rock was very rough, it is on the top of a hill near woods and was very exposed to the seasons. So I repainted the image on a metal plaque, and it is hung there on the same spot.