Poison ivy.
Poison oak.
Poison sumac.
The guy needs to start collecting chow chow dogs.
They are really cute and really don’t like strangers.
The homeless people will break some land speed records getting off the property.
MrEdd, Agree.
Maybe also turn the property into a ‘rehab’ facility for Western Diamondback Rattlesnakes?
Lead poisoning...
Red ants