I've got a 7 foot tall perimeter fence with a wire apron on the ground and the wire apron is covered with heavy rocks. That's for day time, as long as the hawks leave the birds alone. So far (touch wood) it has kept all dogs and coyotes out.
Then the ducks have welded steel dog runs topped with stable panels. Wire floor that extends as an apron on the ground to prevent digging. That has a tarp over it to keep the run dry. That's for night time, to protect from owls and raccoons.
Then they have a fully enclosed coop with a solid floor and welded rabbit wire over the windows so nothing can get in.
What housing are you using and who is killing your birds?
And yes, I agree that it is not a good idea to get more birds if you can't keep them safe. Or you could upgrade your security so that they are safe.