I started raising chickens in Central Oregon about almost 10 years ago. Bend is dry so I never saw pests or raiders due to the scarcity of them finding food in the wild so they were thin in numbers. I also, after trying free ranging the chickens, that neighbors dogs was the worst I experienced catching them for dinner when they wandered over the short fence (not it mattered, they fly higher than that). Even so I built a large run with coop out of 1" poultry wire to keep out what I knew was around but not rats. I lived in a dense pine forest outside of Bend. Hardly ever had any issues of anything getting in and ravaging my flock with what I built. That experience kept me pretty stupid about rats! I started with about 10 chickens and after 5 years built up to about 25. My primary goal was to eat eggs. Since Bend was pretty cold in the Fall, Winter and early Spring, the chickens did not lay much in the long term cold weather. I didn't know enough to make them more efficient layers but I've learned well since then. I finally got tired of the freezing long winters and moved to the Portland area and took my flock with me. Whole different ball game there, everything grows and supports lots of wild predators, large, medium and small. The West side has lots of forests and hills mixed in with the suburbs for them to hide in. I got hit in the first year by a colony of rats that dug into and under my fenced in run/coop and it took me a another year to figure out where so much of my feed was going. I never saw them until they got to be a large colony. Once I became aware and started my own war with them (the clever engineers with whiskers) I learned over a 2 year period that they were a determined very clever animal, not only getting at the feed but weak or sick hens. Several of them can clean the bones off a small chicken in one night. My last couple years since then, I have tried about every preventative method I could think of and what was online. I am a retired engineer and they outwitted me more times that my fingers and toes (and then some). The main thing was first to keep them out. 1" poultry wire will discourage full grown rats but not the teens who get in, dig in and never leave. They do the most damage and hard to trap because if you get rid of the ones in there and once they are gone, more squeeze in and take their place. It is a bit of exaggerated rumors about what rats chew thru. Yes, the tensile strength of their teeth is higher than normal steel and some rats get so determined they chew thru concrete. They are gnawers and extremely patient but they tend to look for easier ways in rather than chew thru hard materials right away and more than not they do!. The best defense is to observe their habits. They certainly inspect yours! Rats don't like to be out in the open so do not have any kind of ground cover near a chicken cage. They like to move up to a barrier and along either over it, thru it or around it. The barrier triggers them to start finding ways in. Rats are the best mammal diggers for their size in the animal kingdom. They can dig well over 3 or 4 ft in one night if they find dirt and even dirt with gravel in it too, I sadly found out. They move what to them is boulders like they are pebbles to us. I wanted to share with you that I fought this war for 4 years and at this point I have so far finally won. I wanted to list the best but simple ways to stop them getting in. 1. Rats do not like asphalt shingles. If you cover dirt with shingles out about 3 ft away from the cage, they don't seem to know enough to backtrack and find the dirt to dig. Put it down just like on your roof, overlapped. The sun will glue them together and they won't slide. If they cannot get thru the fence, they will climb all over it instinctively next. The bottom of your cage won't suffice to just bury the galvanized fencing in the ground. Put 8x16" pavers on top of the inner edge of the shingles all the way around a cage and treated 2x4s on top of them. Staple the bottom of your fence which has to be either hardware cloth or 1/2" hex fencing (called Aviary Netting) to the wood but do not touch the ground. Galvanized or not it will rust and the rats will find those rusted points. They can crawl thru small holes due to the bones in their face is not fixed. The last tip I will leave with you is to build your version of defense and wait with extreme patience for them to find all the weak points and create a permanent patch of fix. There is more in how the whole cage should be built but that's another story. One important overall fact about the intelligence of a rat, they know nothing unless they "discover it" they do not think out and make plans but react to what obstacles they find. If they achieve what they want to do getting past that obstacle, they will remember it their whole life and any other rats who are will them will know it too but only by following the one who first discovered it. Other rats in their colony not there won't know until they are shown. Rats have a short lifetime so if you trap all the rats who have figured out to get in to your cage, the ones to come after won't know what the pioneer group learned. Whatever solution you create to counter what one group learned won't be challenged by the newcomers so quickly but also the new comers won't be so lucky either to discover it. You learn more than they do over time.