I recently built my coop here from prior experience...eh...or maybe inexperience, lol. I built a coop that was predator proof....even down to snakes. I bought some 1/2"x1/2" welded wire and used a ton of staples. Put the wire everywhere you can from top to bottom and seal up all gaps up to 1/8th" wide with expandable foam. This will make it snake proof. From there, I bought some galvanized 1"x1"x18" tall standard chicken wire...dug a 1 foot deep trench around the bottom of the entire coop, lay the chicken wire in the trench and staple it to the bottom board (if yours is metal, use some sort of mechanics wire or even bailing wire) and lay the wire into the ditch....from there, lay big bricks or large rocks down on the wire, then cover it all up with dirt or gravel. Gravel is a good way to make water runoff easily. This method keeps out the digging predators. Around my area there is an abundance of limestone and it sucks to dig down any amount, but it really makes me feel at ease knowing that my hard work will keep my girls safe. As for the actual coop, my coop is all housed in and not part of the run....well, it is when I open the door to let them in, but at night they stay inside and out of the rain/snow/wind/cold. i just make sure the thing is nearly air tight....this is where the expanding foam comes into play again.
Put it this way....build it strong enough to where you can't get into it bare handed (aside from using the doors). If you can't get into it, then more than likely predators can't either. Remember to double latch your doors or find a positive locking way to lock the doors....coons have fingers like we do and they are smart enough to figure out how a lock works if they can reach it. I have two locks on all my doors...one at the top and one about 2/3rds down. Just makes good insurance.
Also, you can put an electric fence around the coop. You can buy a cheap fence charger off e-bay and get the galvanized wire from the hardware store. Use PVC as an insulator and go around the base of your coop somehow and make sure you have at least 3 or 4 rows of wire at least 12" high....tightly strung up and far enough away from the pen that your birds can't get hit from inside. If your birds free range during the day, put a timer on the fence charger. This fence will highly discourage almost any predator.....I don't have an electric fence ...YET, but I have all the materials if I ever have any sort of incident. This method works great for non-free range birds while you are at work and have no way to keep an eye on them during the day while you are at work.
One other thing of added protection during the night hours is to buy a motion sensor/alarm system. This will send a signal to an alarm inside your house (assuming it's close enough) when there is a presence of a critter snooping around. I have two sensors on my coop....each one on the longest side since anything wanting in will travel around the edges to try and find an easy entryway and set off the sensor, thus letting me know it's presence. You can find these motion sensor/alerts on e-bay. They are called "Driveway alert". They work very well, but I think the tone they give off is pretty cheesy, otherwise a good investment if you have predator problems.
I live back in the sticks and critters are everywhere. I have been alerted half a dozen times during the night since I got my chickens (3 weeks ago). If I get an alert, I sneak outside with my deadly accurate rifle (.22cal) and a nice bright LED flashlight.....if I see nothing close to the coop, I look around for eyeballs in the darkness, if I see any, it's getting a piece of lead right between the eyes.....I don't care what it is, if it's a critter out here too close to my hens, then that's too close and if I don't take care of them ASAP, THEY WILL BE BACK. I cherish my girls like family. So far...3 coons, one fox and 2 possums. Lots of (dead) critters around here.
Good luck with it. There are lots of things that can be done to protect your investment.
~Joe
