Color Buffer and Depth Buffer saving

Hi guys. I am drawing a lot of stuff on the screen with OPENGL. I have a background and a foreground. I want to seperate those two parts so when the stuff on foreground is moving, the background should stays still and never redraws itself. So I really wanna save and load color buffer and depth buffer frequently. Accumulation Buffer is probably a solution for fast color buffer operation. How about depth buffer? Anyone can give me some tips? Thanks.