How to: wait for the guard to be next to jacuzzi. Shot the car to trigger the car alarm. Wait for jacuzzi guard to get curios and look over the edge. Wait util he will look down to the car, putting his hands on the glass panel. Shoot the glass panel not the guard. He will fall over the edge landing on the guard bellow killing him. Video here:

There is another way to do it. I'll post it later.