Oh yes they do return....we joke in our neighborhood that all you have to do is worry them enough so they go to the neighbor's....but alas in time...THEY'RE Baaaack.
Here are the best chicken friendly line of defenses:
1. Pick up all feed at night. Store in metal containers. ETA: or use some sort of rat proof feeder, but I can't personally attest see posts above. I have put orange 5 gallon buckets over metal feeders sitting on the ground, and that has kept them out of the feed...until they start chewing holes in the bucket...which you replace.
2. Remove any overgrowth or wood piles that allow them to hide...generally they don't like open pathway, so have plain ground surrounding your coops. ETA: that's harder when the neighbor's have overgrowth and you live by open field/wetlands.
3. Have raised coops with solid structure, especially for chicks.
As chickens still scatter feed, which honestly gets to be impossible to gather every crumb, you'll still get some rats....especially as they start to come out in the daytime to eat chicken feed. (Oh yup, they do). For those you set traps or use poison. As rats get trap savvy pretty quickly, at some point you go to poison.
The Tom Cat bromethelain type poison is repeat eating that thins the blood. It is less dangerous than the first bite neural toxins (which usually have to be gotten through a pest control). It also has very little secondary poisoning if an animal (say your dog) eats a rat that has died from that poison. (Unlike other first bite poisons).
ETA: I've also tried a home-made remedy of plaster paris mixed with bird seed. Make a mash like mashed potatoes and form little soft balls. Leave out for the rats to eat. It clogs their systems as it dries. (Horrible death I'm sure, but sometimes it's a war out there.) That has reduced numbers, and if you mix a lot of bird seed, they seem to eat it. Place where birds can't get to it, but it would take a lot of those balls to clog up a bird or dog.
Beyond that you can get creative....my son and husband plunk rats with a pellet rifle (no one write me nasty responses...we are drowning in rats at times here).
I also got a sweet Rat Terrier from a rescue...he's started a wall with his notches.
And we've had owls and kestrels hunt...however those can also be hard on your birds.
Good luck with your battle. You win a few skirmishes, but with a lot of field and forage around you, especially if the neighbors aren't as careful, chances are you can only thin the population for awhile.
LofMc