First off, if the fox is discouraged from jumping or climbing over the fence, it is possible that they can break through it or dig under. Chicken wire is only meant for keeping chickens in. Regardless, you only need one wire if it is positioned correctly (though more is always better). On my fence the wire is at the top. This prevents the fox from just jumping over it. The wire can either stick up from the top about six inches or stick out away from the fence about six inches. Hopefully you can visualize that. This will prevent the fox from both jumping over and climbing under. Make sure that the wire is not in contact directly with the fence. Also, the fox needs to be in contact with the ground or, in this case, the fence (which must be in direct contact with the ground) in order to get shocked. This is due to electricity wanting to flow to the ground. If it doesn't have a clear conducting path to the ground, it wont shock. Ex. if you stood on a plastic stool and touched an electric fence, you wouldn't get shocked. But if you were to stand on a metal stool, you would. Ahh science. I am about to buy a solar powered electric fencer. This will save cost on electricity/batteries and save the environment! You don't need that much power for a small fence. Just enough to discourage the fox from trying again. Hope this helped.