I've been using this parking sensor (
ReverseGUARD Parking Aid :: Sigma Automotive) for a few years starting with Honda Fit, which I traded in for Insight, and VERY happy about it! No hassle to install, just a small hole behind the frame, and you'll need to remove the plastic tailgate lining from the hatch for the control box and the beeper, that is WAY easier, than removing the rear bumper cover. Not sure about the license plate shape in Netherlands though...