How should I make rocks on a cake?!

Best Answer - Chosen by Voters

Try putting gray food coloring in melted white chocolate and then dipping leftover shreds of cake into it and then let them dry. Then put them on the cake. This should make for some rocky looking pieces. Putting a big cakeball in there would make a boulder looking piece.

Another option is to just forget the cake idea and get your dad a 20-piece bucket of KFC extra crispy and put a toy truck in the bucket.

Chocolate idea I just made up.
http://www.kfc.com

You can buy candy rocks, I've used them before. The color will run if you put them on liquid, but placing them on icing or fondant works. I know Tom's Farm in Corona carries them, I'm not sure if they have a website though.

You may be able to find candy rocks, I've seen chocolate pebbles and jelly bean rocks in candy shops before.
You may also be able to to use fondant to make larger stones or use crushed chocolate cookies as gravel.

You can buy chocolate rocks.

Or use oreas for the dirt than leave soem chucns rather large.

Roll some marshmallows in cocoa powder. You can use large or small ones or a combo.

Brown peanut M&Ms could work, too.

Gum paste