"Reverse"Apron

[Dnar]

Foxes tend to go over, not dig under, if they can't go through. They can jump and climb amazingly well. What kind of fencing do you have?

4' tall 2" x 4" welded wire fencing. I'm planning to add an electric wire about a foot above the existing fence to help prevent jumping. I actually have an electric wire fence around the coop, but it failed to prevent a fox attack a few days ago. I had wires about 3", 6", 9" off the ground to keep predators out and then two more lines at about 3' and 4' to keep deer out of a garden near the coop.

 

[SourRoses]

Sadly, once they're airborne in a jump, an electric fence can't shock them.
That upper strand can work if they're climbing and still in contact with the fence, provided the fence is well grounded itself.

 

[McChooky]

That's a lot of powder for 1000 feet of fencing. Although I wonder if cayenne can help prevent the armadillos from turning my lawn into a minefield.

https://www.motherearthnews.com/organic-gardening/armadillo-repellent-zmaz10jjzraw/

 

[raingarden]

I should have mentioned in the original post that fencing spans about 1,000 ft. I actually need to rent a trencher for another project, but trenching underneath an existing fence seems almost impossible due to the trencher "dimensions".

If you can get a tiller along the fence line then you could plant something that grows vigorously, spreads and mats. Put the apron on top, and let it grow through. Maybe stake the apron down where needed to keep it flat to the ground.

You can cut cheap stakes from a piece of half-inch PVC pipe. Make a notch near the top to grab and hold the wire mesh.