Shooting grey squirrels on large estates requires a plan, a strategy, for approaching how you are going to target the woodlands effectively. A casual stroll may get you one or two, but it is far from effective in terms of serious control and conservation.
I activate around three feeders in different woods at a time and rotate around them through the week so as not to overshoot any one of them. It also keeps the grey squirrels guessing and applies pressure across a broader area.
Once the wildlife camera fails to capture images of greys, the food is not being taken and I don't see any greys across a small handful of sessions, I have enough evidence to suggest moving on to a new location. However, the idea is always to return to these places and re-apply pressure in due course.