Well, if neither rain nor sleet nor pepper spray nor common sense is enough to convince the occupiers that long-term occupation of public places is a bad idea, maybe this will do it.  Annie Gowen writes in the WaPo's Post Now Blog:

The rat population around the two Occupy D.C. camps at McPherson Square and Freedom Plaza has "exploded"since protesters began their vigil in October, according to Mohammad N. Akhter, the director of the District's Department of Health.

Akhter said in an interview Monday that city health inspectors have seen rats running openly through both camps and spotted numerous new burrows and nests underneath hay-stuffed pallets occupiers are using for beds. Both campsites had working kitchens for weeks until last week, but protesters at McPherson Square voluntarily closed down theirs after health inspectors pointed out unsanitary conditions during an informal monitoring visit.