How durable is the string used?

This is a common question and the answer is: VERY DURABLE.  In fact, over the many years we have been manufacturing and selling Chickenguards all over the world, we have had only TWO cases of where the string has broken.  In both of these cases, it was rubbing on the side of the coop!  For those technical folks, the breaking strain of the string is 25kg or 50lb.