I'd definitely put a driftwood in this. Probably sticked to the background behind the land area and moving towards the pond area. Also you must have in mind to chose the wood with the proper size, because you dont want it to make your waterfall and feature look like a water hole after rain This will add more depth to the tank.

Also about the background i'd do a place where i can put plants on higher level, just like in the palu from the picture you linked.