The phrase "porous borders" refers to borders between countries or regions that are not securely controlled, allowing people or things to easily cross through without much restriction or regulation. Full definition
Schwabsky writes: «the fact that so many painters today are working along the broad and very porous border between abstraction and images is a sign that this boundary is, in itself, an object of great fascination. (painters-table.com)
About the only unnecessary tangents here are Heineman's trips north of the border, where American paramilitaries have taken it upon themselves to police Arizona's porous border with Mexico. (straight.com)
The Assistant National Secretary General of Miyetti Allah Cattle Breeders Association of Nigeria, Ibrahim Abdullahi has said the existence of porous borders in the country is being responsible for the incessant herdsmen crisis in some parts of the country. (newsdiaryonline.com)