I got this one randomly after shooting an enemy mine. I only made a token attempt at specifically going after these targets. I suspect that I picked up the majority of my progress during head on runs against other players. If they fire a missile at you it'll probably get shot up during the pass. It seems easy to accidentally gain progress through normal play.
Missiles and mines are targetable and mines have an easy to see red aura around them. Unsure if bombs are targetable but there isn't a lot of time to hit them anyway, so it may not be worth the time if you are trying to grind through this one.