u properly patch them as soon as the start to form to keep rodents out If you are unable to find the source of the openings, ultrasonic repellents will work to keep rodents out 2 Piping, Plumbing and Utility Lines Check around the plumbing, wiring, cable, and other infrastructure that leads out of a house Purpose-placed holes in the foundation can open up, or be too large in the first place Stuff t