I am concerned about the middle of the day attack/rabies possibility. Please be careful handling the fox/the chickens it killed.
There are predator lures and calls available to help you draw the fox to a place where you can shoot it safely (clear shot, away from house and road). I am happy to chat about hunting strategies and techniques (although I am far from an expert)- I have addressed predator problems this way successfully- and need to do another this weekend as well
It is sad to have to shoot a predator. I wish they had more range available to them and could stick to eating the groundhogs! But my experience says once it finds my hens it will come back over and over until I have no hens so I either need to give up keeping chickens or just address the problem.
I have used a .22 rifle with high speed hollow point ammo with good success for fox (the better ammo is worth th $ IMO). I have a youth model rifle being female/shorter arms I find it much easier to handle and aim than the larger models. We have a high speed air rifle for rats and possum but I like the .22 for anything larger.
I personally prefer shooting (direct and you know what you are getting) to poisoning where dosage and availability to other animals makes me concerned that the predator will suffer more than necessary/get sick but not die or that I will end up poisoning something I didn't mean to poison. But it sounds like it worked for go-veggie, so maybe that would work...
You might call any local person who does hunting classes/takes people hunting for pay- sometimes there are experienced hunters happy to have the opportunity to rid you of a predator.
I am sorry for your loss.