The following link will take you to a multiplicity of HN posts describing why the "100 mile Constitution-free zone" is false:
https://hn.algolia.com/?query=Almeida-Sanchez&sort=byDate&pr...
The short summary is: in order to be searched under the border search exemption, law enforcement either needs probable cause (like in any other search), or a demonstrable nexus to an actual border crossing. If you happen to live 5 miles from the Mexico border, the police cannot in fact search you at random, nor can CBP or ICE.