It is not so much our presence that spooks fish as it is drawing attention to ourselves with a sudden movement. So long as the eating end of a fish is pointed in your direction, resist temptation to fire off a quick, desperate cast. The result in nearly every case will be a frantic fish disappearing in a cloudy, disappointing wake. Instead, hold position until the fish makes a turn and cruises slowly away. Then, while its attention is aimed elsewhere, you can make a more patient, calculated presentation across the fish's path.
Noise is by far the greater demon and more difficult, compared to visibility, to control.
Above or below the surface, sharp sounds spook fish. Even if they can't see what caused the disturbance, instinct tells them to make tracks. To a fish, it is better to run from a false threat than sit still and hope that nothing bigger and hungrier is on your tail. Boats make noise, some more than others, and serious flats fishermen are as concerned with hull slap as they are with livewells and poling platforms. Pay attention to the sounds of water against your hull as you drift or pole across a flat.