Should have mutated medical or insect. That’s on you for going squid.
In seriousness I’ve never seen them bash down a log wall so I’m sure stone will be fine. I think they have high night vision though, and with their ranged attacks they’re definitely a pain in the ass. They make great armor though, and at least their fat is good for sausage.
EDIT: Since you’re in the sewers too you can line the narrow passages with nailboard traps and the like, just to cause further difficulty for any that wander your way.