I just wrote a research paper on vacant, blighted lots in Atlanta and their effect on neighborhoods.  Turns out the city actually does have a whole system in place – in theory – to keep them from happening.  There is stuff in the code about structural problems, garbage, attracting criminal activities, graffiti. . .you name it.  You can even get in trouble for letting vines and vegetation grow enough to house vermin: rats, flies, lizards and snakes.  The Atlanta code doesn’t seem to have my problem with squirrels.  But lizards?  Look out.  Lizards are a menace.