Chicken tractor run security.... (digging preditors)

I'm building a portable coop...It's going to be on unused flower beds so I don't have to worry about grass getting killed. I originally had a tractor in mind but this is turning out to be more like a mobile home. I still want to be able to rotate it monthly (or as needed). So I don't want to bury wire in the ground to keep the chickens safe from predators who might dig under the coop. I've found topics dealing with this problem where people have recommended a wire skirt staked into the ground.

How many of you peeps have done this? Your experiences are appreciated Also if anyone recommends any other ways to make a portable run safe from digging predators. I was thinking about running an electric "hot" wire along the bottom perimeter and looking for something at Home Depot that may have been designed to keep dogs from digging under fences. Thanks in advanced! I'm sure I'll post pictures soon. :-D

~ cowchipss