Workbenches are your friend. Try moving out systematically from your base, digging down just enough to cover up a workbench with wooden floors so things can't immediately get to it. Ensure that the area that shows up with the hammer out is overlapping the radius of the newest workbench, and keep moving outwards. While mobs will wander in from the outside, you put enough ground between the edge and your base that mobs will never bother you except in events.