There are to many to hunt them with an air rifle anyway i think. They will win in my opinion unless you try these methods and say this because professional exterminators all over have been having a hard time eradicating rodents like voles, Rats, chipmunks, and packrats
Traps in my area work fine on voles but not on rats or pack rats. Pack rats are very aggressive here. The pack rats here attack live animals like rabbits at times and eat them. Poultry is their favorite food once they get large. Many people blame cats for what pack rats do. House cats even.feral fear pack rats. Thankfully we have coyotes , hawks, and owls but remember they dont discriminate on what they eat. So a coyote will eat your house pets. If your coyote population is higher like mine is remember my pets sleep inside for yheir protection at night. We have eagles or falcons at times but they are so rare like bobcat right now im not including them. Racoons and possums are rare right now. We have had a coyote with a strage bark so he might be part wolf or dog and he is an aggressive hunter at dark every night. If for some reason you must use traps because baits will be eaten by good animals here is what i do #1 set traps in clusters of 5 or 6. Learned smart animals defeat traps so set traps they back into outsmarting your other traps they wont see that coming they are watching their front not their back. So a trap in the center with bait but 5 or 6 more traps all around the baited trap. #2 i used victor traps before but found modern snap traps are cheaper and better.
A really great method but requires a big commitment on your part is a small rat terrier or similar breed. My friend wiped out all of his rodent problems with a terrier.
If not convinced see this thread You win some you lose some with rodents! . This is my dog thats with my ex fiance now. He murdered many rodents but its rare footage to capture him doing it. He ate them so fast it was shocking.
It might be worth noting for some people my barred rock chickens cured me of eating eggs many times when they attacked rodents or snakes. They are a meat eating breed that actively hunt voles but they will be hunted by large packrat communities. You can see the size of the packrats on this thread Rodent control - #2 by clarkinks
Dry ice is a great idea consider running exhaust off your muffler down in the hole. In my experience water never worked or fumes of any kind in my area im not sure why. All that said i dont have chipmunks or squirrel because the predators like coyote who eat vole as their primary food are left alone on my property. Snakes are their natural predators but my guess is you have few snakes since population is higher there. The prey remain long after the predator is wiped out.