Let's take a look at some basic firearm safety rules. Never shoot at hard objects or flat surfaces such as:
Water

Hard, flat ground

Rocks

Trees

Solid metal objects not designed for target shooting

Bullets can ricochet or bounce off of hard objects and flat surfaces, sending the bullet somewhere you might not want it to go.

Rocks can explode into many pieces, going in all directions.

You're responsible for where your bullet ends up. Never shoot at hard objects or flat surfaces. Bullets can ricochet, and flying pieces can hurt you or others. Always know where your bullets will go.

Remember, firearm safety is your responsibility.
--Larry Potterfield