Hi, welcome to BYC!
Agreed with @TheTwoRoos When I go in to check for parasites at night and take the birds off roost, the rooster ducks down and acts like he isn't there. He avoids trying to become dinner himself. So, he isn't completely stupid enough to sacrifice himself. Also, against a fox a roo does not stand a chance... so he would be gone as well.
That's what people don't understand is that often times having a roo doesn't protect their hens but rather becomes the dinner of said predator, essentially a stand in the hen that would have otherwise been lost.
Thing is... that fox KNOWS where to come get his easy meal.... and WILL be back until your flock is either secured or gone.
I love roosters and have a few. But IMO, they are NO better protection or warning than ANY of my top hens, who I've seen knock an overly amorous cockerel off another girl and make sure she was OK AND fight 2 dim mannered cockerels at the same time and won to teach them some respect. So when people say they want a rooster to protect their flock... I mostly roll my eyes (to myself), as that simply isn't reality.
Of course their are good roosters. And MANY have given their lives trying to protect a hen! And their level of protection DOES vary with their level of maturity. They become much better at what they do as they gain maturity. But NONE will ever be a good match for a fox... who I'm guessing is hunting in broad daylight? I suggest you arm yourself or set a trap and be prepared to dispense of the predator on a manner that does NOT include relocation which is often illegal and always cruel!
I am sorry for your loss. They always get our favorites first.
Good luck correcting your defensive line, ASAP.