Chicken fencing help

Picture for tax. This is only their supervised few hour a day turnout area for now as they’re very young, but I’m about to set them up a large run.

I was going to buy 6 foot 19 gauge 1/2 inch hardware cloth and bury it going outwards to protect against digging predators. However, how should I fill in the area? Would gravel work or will it get dug up too easy? Should I use soil? I also had holes dug for wooden fence posts, so same story for that. Gravel? Soil? How can it be stable? TIA! Main predator worries fox, raccoon, opossum, weasels, fishers and hawks. So mainly rodent based, not so much coyote or dog. I will be covering their run with netting.