First port of call should be how do people who behave like that get the jobs....so if the background checks fail then and one or two still slip through then the management of the care home needs an overhaul . Covert cameras may be replaced by voice recorders on all staff so what they say and hear is always recorded...no ones privicy is affected. 

Next what about the carers that do the home visits ...are there any people in the system being abusive to elderly there ? again microphones.