We're surrounded by predators here and I made it until this year without a single episode but this year I've had snakes, owls, and hawks that have successfully attacked. It's a risk you take when free ranging your chickens but I also feel like free ranging is healthier for them. We're working on plans for a large fenced area with a netted top since predators seem to be worse from the sky during the day here and we already have a very secure set up for nights. Having access to bushes and such to hide under helps too. You'll find what works best for you and your chickens. Do you have a hardware cloth skirt around the base of your enclosed area? I only ask in case whatever critter is going after your chickens is a digger you may be setting up an all you can eat buffet.