The scent thing has to do with city vs country fox. Fox in urban areas won't care about human scent, since it's every where. Country fox that don't "have" to encounter human scent for food... are going to care. Animals use scents as guides. Country fox, know human scent can mean bad things. City fox... human scent usually means easy food. So the trapping of a fox depends on the type of territory the fox lives in.
Live traps can work for urban, but for country, the less humane leg trap or a snare would be more likely to work. Still no garentee.
If you do opt for leg traps, be sure to check it OFTEN, and bring a gun or something to finish things. No creature deserves to suffer.
Are you hanging the bait in the live trap and/or setting it away from the back/sides to prevent easy access?
I never bothered to trap the fox around here, we had a pair of them who would occasionally come around in the afternoons for the chickens, but the chickens were never surprised and got up into the bushes fast enough. After setting my cattle dog on them a couple times, they quit showing up. Never got easy food, dog always set out... chicken hunting never paid off for them.
Fox are only bad when they succesfully catch a chicken. If they never get the chance, they'll never associate your chickens with easy food.
The biggest mistake is not setting the food right on the trap, and giving them "free" meals, that will definately keep them in the area, and you'll never trap them unless they make a mistake.