It won't be predator proof. Snakes at the very least could fit. If there's any mustelids they could get in as well. Raccoons could reach in. Bears can go through anything but they're a special case.I was hoping for a predator proof run. I've seen a skunk up on the hilltop where we live. And we see an occasional dog wandering around. Neighbors have reported snakes, but I haven't seen any.
I inherited the fence wire we have, so I had to use my calipers to measure the specifics. The holes are 2" x 4" and it's 14 gauge wire.
You could use it as a foundation layer of the run, but you'd still need HWC or welded wire no wider than 1/2" securely attached to seal things up.