You can invest in a live trap. You can get a set of 2 at the TSC for around $30. Bait the larger one with some chicken parts, table scraps, or sardines. I've caught a lot of feral cats and possums that way and it will probably work for your fox.
If you can't buy the animal urine, I've heard that you can pee around the coop and it will work... Just make sure your neighbors are not looking out the window when you do this!