cover your backside/behind/rear idiom very informal (also UK offensive cover your arse); (also US offensive cover your ass/butt)
（做某事以）保护自己的利益，不让别人抓住小辫子
to do something to protect yourself from blame or criticism in the future
He'd do anything to cover his ass, including lie, cheat, and murder. 为了保护自己他会不择手段，包括撒谎、欺骗，乃至杀人。