Chipmunk problem? What chipmunk problem?
Go the your local humane society or equivalent. Tell the nice lady at the desk you need a cat for a companion. (Fer gawsh sakes don't tell her you want it to kill something; she'll have conniptions, won't let you have it, and will blacklist you.)
Pick a nice looking, biggish tomcat, mebbe half-grown. Get it fixed on the way home. Unfixed toms tend to "mark" their territory, in a way that your wife won't approve of in the house.
Toms are much more friendly toward humans. Cat people call the females "queens" for a good reason.
Treat it nice; feed it regular but not too much; a fat cat isn't as agile.
Bingo, you got an automatic chipmunkÑand any other small mammalÑkiller that's quiet, effective, loves its work, is on the alert 24/7, is legal in all 50 states, and as a bonus will sit in your lap while you read the paper, and purr and expect to be patted.