I got to a friend's house one time just as he was getting ready to butcher a hard shell turtle. Best I remember he had the head cut off and then nailed the turtle to a tree by its tail. I think he also cut the underbody shell away. He had me hold a leg as he worked around it. Even though the head was gone they still can move their legs. And let me tell you, they are strong. This was back in the mid '80's so I can't recall all he did. Stripernut's method sounds like it might be easier.