Collocations for flank - noun

left, right
north, northern, etc.
lower
the lower flanks of Vesuvius

attack
They decided to attack their enemy's southern flank.

cover, defend, guard, protect (all often figurative)
expose (often figurative)
This meant exposing his flanks to his political enemies.

along a/the flank
along the eastern flank of Greenland

down the flank
a beautiful pass down the right flank

on a/the flank
The army was attacked on the left flank.