An apocryphal story, but a good one...

I have heard tell of a certain museum in a large urban centre that deals
with "Orphan Donations", any package on their premises without the
signature of a curator on the temporary receipt, by calling the
municipal police bomb squad and asking them to remove it, with the
remote controlled tank, water cannon, et al.

Not an effective solution for exurban sites, but it sounds like it would
work.

Usual disclaimers,

Craig d'Arcy