1. Wearing gloves, mix 15 cups/120 oz of concrete with water in a large bucket with a mixing rod.
2. Place the corner of a durable trash bag into a plastic container. Fill the corner with about two cups of concrete, and pat the sides to release any air bubbles. This will be your hedgehog's head.
3. Place the bag into a larger container, and add the rest of the concrete. Pat the sides for 5 more minutes to release any air bubbles.
4. Twist the bag shut, and place rolled up rags on either side of the concrete bag to keep it from flattening.
5. Let harden for 2 hours, then press the eyes and brow into the concrete (on the corner).
6. Let dry for at least 24 hours before cutting open and sanding down.
7. Cut a plain doormat into a 15-inch x 14-inch piece (give or take, as size and shape can vary).
8. Cut three 45-degree angle triangles into the top of the mat. The center triangle is roughly twice the size of the other two.
9. Cut the largest triangle at the bottom, and two medium triangles on the sides.
10. Apply heavy duty glue generously over the edges of the mat. Lay the top of the mat over the concrete, and fold the three triangles together so they sit flush with the brow or your hedgehog. It is easier to glue one side at a time. Secure the mat in place with tape, or by wrapping with string until dry (about four hours).
11. Trim the back corners of the mat into curves, and glue the rest into place so the mat fits like a turtle shell.