I try to give my foxes as much to do as I can. Some of the things I do to keep them happy and busy are:
-I give them Kongs filled with different food items from vegitables to scrambled eggs to kibble to cooked meats.
-In their enclosure (since mine has a plywood floor) I gave them a couple tires and filled them dirt so that they can dig.
-I fill styrofoam or plastic cups (or even ice cube trays) with chicken broth and a variety of veggies and meats and freeze it. Then on hot days I give them these popsicles to chew on and cool down.
-I try to walk them as often as I can. Foxes have lots of energy and if they don't get to use it they become destructive little critters. A harness should be used for walking the fox.
-If I can't take them for a walk I put them in my big play run (10 by 35 feet) and let them run around for a few hours.
-I hide bits of food all around their enclosure so that they have to forage for their food like they would in the wild.
-I give them raw chicken bones to chew on and hide. Never give them cooked chicken bones!