Begin with a 12 inch by 4 inch square foam. Draw or trace a slightly oval shape for the shell of the turtle and carve it out with a serrated knife, rounding it off just as a turtle shell looks like. Use one of the extra pieces of foam to sand the edges of the shell, leaving the top portion rough to add texture.
Cut six, 2-inch by 4-inch pieces of foam for the limbs, head and tail. Carefully carve each piece so that one end is rounded off. For the tail piece, cut it into a V shape. Using a scrap piece of foam, sand the rounded edges to smoothen them.
Texture the turtle body using the point of a potato peeler. Scrape out a pattern of squares on the top of the turtle shell. For the head, scrape out eyes and a line for the mouth. Draw five lines on each limb for the toes of the turtle. Yes, it is true, turtles have five toes on each limb. The amount of detail you add is up to you.
Before you attach the head, limbs and tail, determine where you want to place them by using toothpicks, and play around. Once you have determined where to place them, use the potato peeler and carve out indents in the shell. This will give the shell a more realistic look.
Using white glue, attach the head, limbs and tail while leaving the toothpicks in to add support. Allow the glue to dry per the instructions on the package.
Paint your turtle using a latex-based paint. This is important because some other types of paint will eat away at the foam. Allow the paint to dry per instructions on the paint can. Once your statue is covered completely with a latex-based paint, you may add detail using any of the other types of paints, sparkles and other designs.
Preserve your turtle statue by coating it with polyurethane. This is a good idea if you are going to place it somewhere where it will be exposed to direct moisture. If you are making a turtle statue for a stage set, you wouldn't need to coat it.