Good tips but the whole "angle of incidence is equal to the angle of reflection" thing isn't quite true because no surface in BF3 can reflect the laser beam in fact you can't even see the beam if it's further than like 2 meters from the gun, you can only see the dot...

So if an enemy comes through that tunnel he'll know you're on the left side but he won't know where exactly on the left. You could be on the second floor of that building he would see the same dot on the wall...