When setting up a landing zone for a medical transport helicopter, you should:

Using weighted cones to mark all four corners of the landing zone (LZ) is the correct answer because it provides a clear and visible perimeter that can be easily adjusted and secured against wind or other environmental factors. Weighted cones are typically brightly colored, which increases their visibility, making it easier for the helicopter pilot to identify the landing zone from the air. This approach also helps to keep bystanders at a safe distance, promoting safety for both the medical team and the surrounding public.

Additionally, having a defined perimeter helps ensure that no unauthorized personnel or obstacles are within the landing area, significantly reducing the risk of injury during the helicopter's landing and takeoff. This method offers a practical solution that is commonly implemented in emergency medical situations requiring helicopter transport.