How do turtles protect themselves?

Some turtles, such as the Musk turtle use smell to make them seem unappetizing. All turtles can hiss to appear threatening and many will bite if you get too close to their face. Also, another (rather obvious) method of protection is to tuck all soft areas; their head, feet, and tail, close to their body and use their strong shell to protect them from teeth and getting crushed (usually).