@Ernest Bywater
don't allow anyone else to set up any wi-fi within their grounds
This is obvious, but doesn't actually block (as Capt. Zapp wrote) a wi-fi system brought clandestinely on their grounds.
[...]some cheap units now available to broadcast low power, short range, garbage to disrupt wi-fi signals near them
I thought about creating 'white noise' but dismissed it at too expensive and too problematic if it affects the neighbor's wi-fi. He will sue them if his wi-fi security cameras are disrupted by the white noise coming from the neighboring facility.
Still unclear how this all would affect cellular devices (cell phones aka mobile phones), they work with other frequencies and higher power.
HM.