Strip of light, laser projection or whatever

You could try a basic LED security light with a sensor like the ones we all have outside our back doors etc. Then take a piece of aluminium or tin or even heavy tin foil and cut a super fine slot in it, the tape that over the light, then aim it towards the ground. That will project a line onto the ground. It will be sharper closer to the light and blurrier further away, but should work.