We were never meant to witness their demise. Many incidents have happened in my yard which I have felt very guilty about, but when giving it a lot of thought, these may not have been accidents at all. Suppose you come home and find your turtle or tortoise dead. Here's what I have observed over the years. With turtles and tortoises, it is the survival of the fittest that rules.
Accidents DO happen and they happen to people too.
Keep your bermuda grass clipped short because tortoises and turtles become easily tangled in it and do not know how to back up out of the mess. Sometimes your neighbors have sprayed poison along the fence line or into their trees and the resulting fumes can kill your turtles and tortoises very quickly. Tortoises can be flipped over by other tortoises or even the family dog. Remember not to have any poisonous plants in your yard. Once they pass three years of age, their survival rates get much better.