Your city neighborhood has Bobcats? They're nasty. I'm so sorry to hear about your losses. My DD lives in the suburb city but her property butts up against a natural local preserve for hiking and trails - it has attracted Coyotes, Lynx, Bobcats, once a Bear, and a couple years ago a Cougar! Not to mention smaller pests like Rattlesnakes, Skunks, Coons, Possums, Wild Rabbits, Deer, loose Dogs, Hawks, etc. They've caught photos of several wildlife critters on their night camera.
I'm further away from the Mountain behind us and have been fortunate not to have critters like Skunks or Snakes - but that doesn't mean there isn't danger from someone's loose Python or Boa pet or the city night critters like Coons and Possums. We all need to assess our property for local predators and build accordingly. The key to our 4 hens' survival in our little cottage backyard has been several scattered shelters, doghouses, and popup canopy and we plan to add stickery evergreen, roses, and berry bushes along the fence line - all for the girls to hide/snooze under during the daytime. We have a giant flock of neighborhood Crows that are wonderful at leaving our chickens alone and chasing off the Cooper's Hawks (chicken hawk). I never cared for Crows until I learned how valuable they were at chasing off predatory birds. The Crows don't even bother our vegetable beds.
I've seen chicken tunnel photos and videos too. Sounds like a neat idea if one can be constructed sturdy enough to keep out digging canines like Coyotes, Foxes, Dogs, etc. We are getting rid of our 60-y/o chainlink fence and replacing with a 6-ft block wall with added privacy fencing to make it even taller. Won't keep out the Hawks but will make it difficult for digging critters to enter!