irk

A guerilla is a small force fighting against a larger one. Guerilla activity is rampant in that country.

chetniks

It is not that hard to use guerrillas in a sentence.

See, I just used guerrillas in a sentence.

The guerrillas are attacking!

Counter-guerrilla warfare=anti-guerrilla warfare.

It means fighting (or combating) guerrillas with methods that are effective. Using the old example of, "it takes a battleship to sink a battleship", the proven method for counter-guerrilla operations is "using guerrillas to hunt down guerrillas", such as the Special Forces, SEALS, and Snipers, etc. are trained to do (or at one time were trained to do).