I've never been a fan of "themed" tanks or decorations of any kind in the tank at all. I always like to have my tanks as natural looking as they can be with 3dbg's and rocks and wood and fake plants like silk ones that look more natural and realistic. About the closest I came to decorations was about 6 years ago when I got back into the hobby again I found a fake crocodile skull that looked very realistic. Even then though I just didn't want it actually "in" the tank. So I did something a little different to incorporate it into the tank & stand build.
I built the canopy as a viewable underwater scene by doing some foam work in the canopy like I do with my 3dbg's then used cut mirrors on the underside of the top and lit it up with some cold cathode blue lighting so it gave the inside of the canopy an underwater look. A lot of people that saw the tank at first thought the top part was part of the tank as well so it worked out pretty cool. That's about as close as I have ever got to decorations though.
I built the canopy as a viewable underwater scene by doing some foam work in the canopy like I do with my 3dbg's then used cut mirrors on the underside of the top and lit it up with some cold cathode blue lighting so it gave the inside of the canopy an underwater look. A lot of people that saw the tank at first thought the top part was part of the tank as well so it worked out pretty cool. That's about as close as I have ever got to decorations though.