You seem pretty secure! as far as predators, I have the same problem. Put out a game cam and a trap. Game cams are reasonably cheep. I got mine for about 30$. You just need something to take pictures so you can see were the animal is getting in. For a trap I tried many but my absolute favorite...
I have Arecandas and Americandas ( however you spell it ) they are pretty good layers and the best part is THEY LAY GREEN EGGS!. And they are absolutely adorable!! the have fluff on their neck and cheeks :,)