Depends on the disposition of the individual fox that encounters the set. I sure have caught fox with coyote urine. I am also sure some have shyed away from it as well. I don't think greys shy very much from red urine. If concerned use red urine. When targeting coyotes I do like to use coyote urine. Hope this helps.
The difference between dreamers and achievers is action.
One try is worth a thousand guesses.