When hunting marsh bucks scout in the winter/spring and pick your tree then. Find their bedding. Look for rubs on trees in the islands by the beds. Hunting the beds can be successful but don't over hunt it. You may only get a couple hunts before he is on to you so make them count. Dont go to high in tree stand, you dont need him busting you from the ground because suddenly there is a strange lump in a tree there wasnt before..Getting just high enough to see to shoot works best. Get in early,go slow,very slow. You cant be sloushing around in the water as they will hear it. A moderate breeze is an advantage as it will help with noise. Morning hunts are out. Only hunt evenings. You get in there in the morning and cant get a shot odds are you spook him getting out.Make sure your entrance is downwind. Takes a lot of patience but is doable.Dan Infalt has an excellent video exculsively on hunting marsh bucks worth every penny. He has his own forum full of info on this type of hunting.
http://www.thehuntingbeast.com/