I never used cover scent for Fox.
I have used a scent for Coyote calling. I would spray scent in the air, not on me.
I experimented with different odors for 13 years. I saw Coyotes stop in their tracks, adjust the face and nose to my odors. Some took time to decipher the odor, some stopped briefly and some didn't stop long enough for a shot.
Nowadays, the term for this method is called 'misting', a term I didn't hear about back then and didn't know western hunters used scents from time to time.
I don't rely on 'misting' for Coyotes, but in some setups it is the thing to do.
Goose, If I used Skunk essence for calling Coyote, our local Coyotes would get a whiff then stop with nose to the wind and ponder why Hern hung Skunk scent in the brush 10 yards from his setup.