You can never say never but in my opinion foxes sometimes shy away from coyote urine, on the other hand you can catch fox and coyotes on fox urine. Nothing is concrete with coyotes they are crazy.
I’ve just got a spot I hunt where I always see a grey fox. He’s had a den right next to my blind for years. But I get pictures of a huge black coyote I want out of there. I can choke stick the fox to release but I’m thinking the yote might get to him first.
You can never say never but in my opinion foxes sometimes shy away from coyote urine, on the other hand you can catch fox and coyotes on fox urine. Nothing is concrete with coyotes they are crazy.
x2. research and experience tells me if you had to buy 1 urine, it would be red fox urine. but it's good to mix/change up your sets and throw them a curve ball time to time.
I think using coyote urine would be a first good step to try to deter the fox from stepping in your trap. The other thing that would help is adjust your pan tension so its a bit heavier. I generally use around 4 lbs. and catch both grays and coyotes. Running 6-8 lbs. would probably select only for coyotes as that is about half the weight of a gray fox which should not set the trap off.