What to do: If you find out ahead of time, grab a handful of neighbors and (politely) appeal to the owner to find a renter who better fits the block. "After all, a nice, stable family would surely be preferable to the landlord, too," says Shelley Blood, neighborhood-relations officer for Hillsboro County, Florida, home to three universities. Your group could even pitch in to pay a few months' rent while a tenant is located.
How to keep this from happening to you: Put together a petition for a local ordinance tightening rules on how many unrelated people can live in a single home. "Any existing renters would be grandfathered in," says Blood, "but only until those particular kids moved out."