I know at my house, they never get the chance to get in. For example, when we were still building our house, we decided to stay out there one night. In the middle of the night, my wife tells me she hears voices. She's kind of a crazy sleeper, so I thought she was just talking in her sleep again, but then I heard them too.
I loaded the shotgun, 12g Winchester pump, turned on the outside lights (I have a LOT of outside lights) walked out on the front porch in my cowboy hat, boxers, and boots, popped off a shot into the air, cocked it again and asked, "What the fck's going on out here?!"
Needless to say, they dropped their joints and bottle of schnapps and took off running down the driveway. They have yet to be back, and that's been 8 years ago.