Rats can eat through concrete, if they know/smell a food source on the other side. I have had to go to many grocery stores and have my guys 'try' to repair where they have eaten through concrete, concrete block, etc... Their teeth grow constantly and they must chew to wear them down...
Squirrels can be very destructive, more so than their hairless tail relatives, and more determined. You basically need to exterminate...
Most are creatures of habit and will typically use the same path. If you can locate it, that is where you set your traps, preferably outside...
Personally, I would not eat a squirrel caught/killed anywhere near civilization. Rabies can be terrible thing... ¡buen provecho!