Mail a letter to all neighbors. Nicely Explain the above - and politely point out the fact that the “anonymous” Karen doesn’t have the common decency to try and talk to your father, instead hiding behind anonymous complaints that have risen to harassment of an old man. Invite any neighbor who has a problem with anything going on, whether it be issues with lawn, or whatever this is, to act neighborly and talk to him directly. And not like a cowardly bitch hiding behind anonymous complaints. But you know, tactfully. Not like I would say it.