I used to fly helicopters to the rigs in the north sea out of Denmark. We would tell the pax to remain seated with there seatbelts done up until the blades have stopped turning and the doors had been opened. The Danish pax would start un-doing there seat belts as soon as we taxied in. After a while, we would advance the engines back into flight and sit there until they had strapped back in again. It only took a couple of times doing that until they realised we were not joking. Worked a treat !!