If you are trying to discourage digging predators, one of the most effective, relatively easy and inexpensive options is to run an apron of chicken wire all the way around the pen. You simply roll the wire out on the ground and stake it down in place using landscape staples (heavy wire "U" shaped pegs).
I live in an area with pretty much every known predator except bears. Since I began using electric fencing (I use poultry net moveable fencing) I haven't had a single loss, nor any sign of effort to get in. I spent what felt like a lot of money on the electric fencing, but I love it -- as it has not only been effective, it allows me to easily move my animals to different grazing areas.
So here's what I do for all of my animals: A night pen that is made from 6' fencing (I actually use dog kennels, with hardware cloth attached to the sides), covered with roofing or wire fencing, and an apron of chicken wire around the base. I use this approach so that I don't have to close them inside a house at night. All of this is surrounded by 48" electric poultry net (to create the daytime 'barnyard'). I also encourage my dog to wander the outside of the space, marking her territory. No losses in the past 5 years since using this approach.