yea i was thinking about the problem with laser not reaching long distances through water, but if you just used a rope that doesnt float instead of it than the fact that is sinks proves nothing so it hadf me thinking for Quite a while until i finnaly found a better solution (still more theoretical than practical but i've always been a man of theory). you use a "rope" that has the exact same density as sea water :D that way it neither floats nor sinks, it just kinda hangs around in the middle of the water. of course as you go deeper water gets a bit more dense so the rope would eventually bend