Lay some chicken wire flat on the earth all the way around to help prevent predators from burrowing in. The Geo fabric is a good idea. Been my experience when they get older they spook easily and can hurt themselves running/flying into the wire. Put a lid on the enclosure. Have as little contact as practical with your birds, the wilder they are the better. You can try releasing after the feathers have grown in after their first molt, around two months. But I've found later is better, after around 3-4 months or even later. It helps if they have an enclosure large enough to fly some. I put some cover in my enclosure (a brush pile) so they can hide when I show up. Trains then to go to cover and helps prevent injury from flailing around.

The mortality rate is really high on my releases, maybe 10% last through the first winter.

A single Weasel will kill them all in a single night. Weasels are like Rats, if their head fits through a hole the rest of their body will follow, it doesn't take much of a hole.