Lock it down
From Rap Dictionary
interjection
lock it down
Keep dancing like that. "lock it down" -- Nelly (Over and Over)
this term has many different interpretations, but in this instance (and most)it means to take full control of a particular situation. Basically, to take something over.
In prison, "lockdown" means everyone has to return to their cells for the night and all doors are locked. So "lockdown" has come to mean "in complete control."
I thought this phrase referred to locking the bolt forward and down on a rifle (chambering a bullet).

