If you are making props for a play or wish to decorate a themed room with rock cushions, use simple techniques that produce quality finished products even without extensive sewing experience. Felt is a very easy-to-find, inexpensive fabric that can be found by the sheet in a multitude of colors in fabric stores, craft stores and online. It doesn't fray, either, so it is an easy fabric to work with.
Draw a rock outline on grey felt, using a fabric marker, in the same shape and general size that you wish the final cushion to be. Allow 1/2 inch extra around the perimeter for the seams.
Place the gray felt directly on top of another piece of gray felt and secure it with sewing pins.
Cut the drawn rock shape out from the double layer of fabric. You should be left with two identical pieces.
Secure the identical fabric pieces to each other using more sewing pins.
Bind the edges of the perimeter of the fabric using a needle and thread or loaded sewing machine. Stop sewing when you have about 1 inch left of open space.
Turn the felt cushion-case right side out through the hole you left to hide the stitches. Stuff the cushion with cotton stuffing through the hole until it is packed, so that it looks as rock-like as possible. Some lumps and bumps are okay, as this can make the cushion more realistic looking.
Sew the remaining inch shut on the cushion.
Knot the thread and cut the needle away with the scissors.