You’d achieve it by poisoning the well. You’d make a cultural reflex to reject the information. It wouldn’t be that hard because the information is extremely disturbing. Alien intelligence is a terrifying prospect. So people want to reject it, and you encourage that through cultural engineering to ensure it’s a taboo subject worthy of ridicule.

That basically nullifies disclosure.

Unlike the Manhattan project, the alien coverup is leaky as hell. It make sense considering it’s ongoing for many decades with no end point in sight.

The secret hasn’t been kept. It’s just been rendered impotent by sterilizing curiosity about it within the culture. The secret has escaped prison each time. And every time it has stood dully staring at an empty plane extending to infinity in every direction.

Instead of containing the beast we just removed its food supply. The only place the presence of aliens can be contended with is inside the interface program. The rest of the world has been inoculated against any resonance with the thought of aliens being present. We just can’t process it as a reality.

The secret has leaked countless times, to no effect.