mind your back(s)
Make way or be careful because someone behind you is trying to move past you. Mind your backs, we're coming through with an extremely hot pot of water!
mind your back (or backs)
used to warn inattentive bystanders that someone wants to get past. informalˌmind your ˈbacks!
(informal) used to tell people to move out of your way, for example when you are carrying something: Mind your backs! I’m coming through!