Biggest killer of fox in this country are vehicles and sarcoptic mange,leastways thats the findings of Stephen Harris(doctor)of Bristol University,one of europes leading experts on Vulpes vulpes,though I always found anything from a .17hmr to a .243 was equally as terminal,fox are a pest plain and simple,seen them taking both lambs and piglets,but the most effective way to control the population isnt riding to hounds,its night shooting or snaring,both legal methods.