In urban areas and on the water there are many reflecting surfaces. In day light, moon light and any other source of light casts it’s shadows. To learn to use those as well as the line sight stand in front of a large mirror or hold a mirror in your hand and stand with your back to your partners. Now using what you see defend yourself and see how you work and learn. Later on you can use the shade people cast as they walk to walk away from unwanted touch or toward someone without making eye contact (it is more noticble). There are many variations. THere are but a few.