Omgosh, I'm so sorry for you'r loss...I lost almost my whole flock once to coyotes.... 2 out of 8 survived... I couldn't bear losing my rooster(s).
Sorry about your Rosters. Not suggesting anything but if i even saw a fox, led alone one killed one of my chickens i would whistle it up and... *Take it to a better place*-- with a "SHSPEECH-CRACK".
Thanks! I have been trying to get the fox i go out every morning at sunrise and sunset with a shot gun and .17 i even have a call and it doesn't come in it's the smartest one yet.