Its not always easy but any building can be mouse proofed. For years, we'd catch multiple mice in traps inside every week and couldn't figure out how they were getting in, but then inspired by this video, I built a mouse house with cotton balls, bait, and $10 of fluorescent powder. Sure enough, within a week there was a trail of fluorescent powder that could be tracked with a UV flashlight down a door frame, across the floor, and over to very small gap between the carpet and the wall where the sub floor wasn't cut tight to the log walls. After filling this gap there were no mice for while, but after a few months they found a new path. Repeated the process, and tracked them to a gap around the water heater vent: they were actually climbing up through the channels of a metal roof, and then down along the vent. After blocking that off, we have been mouse free for 3 years.

This is a log home surrounded by woods more than a quarter mile from the nearest building. If it can be mouse proofed, anything can. The only 100% foolproof method is to fully seal your house with no gaps a mouse can fit though.