What word or phrase does your mother always say?
barrier bar·ri·er (bār'ē-ər)
A structure, such as a fence, built to bar passage.
A boundary or limit.
An obstacle or impediment.
Something that separates or holds apart.
Something immaterial that obstructs or impedes behavior.
A physical or biological factor that limits the migration, interbreeding, or free movement of individuals or populations.