Well when yer sittin' back enjoyin' Chip & Dale, pull up the ol' Internet machine and brush up on rodents:

http://www.cdc.gov/rodents/index.html

http://www.cdc.gov/rodents/diseases/direct.html

http://www.cdc.gov/rodents/diseases/indirect.html


Squirrels, rats, mice, & chipmunks are persona, err rodent, non grata around here. The potential diseases they carry and transmit give us enough incentive to eradicate them at every opportunity.

Seems like you've already got your answer - they're up under your concrete patio making nests.