My sandbox 

my space or business that someone else feels they need to manipulate or medel in

confrontation: "bitch...this is MY sandbox and I did not invite you in to play"

My sandbox by Ginalee April 2, 2008

you don't know my sandbox 

Away to tell someone they don't know your space, or they don't know your business.

You don't know my sandbox.

you don't know my sandbox by Jenn N Davin July 20, 2018