Yup, that's a Diamond Goby. I had one myself...very active and cool fish. Although, I found myself blowing sand off my corals housed on the sand bed at least twice a day (to avoid irritation). On top of that, my goby would constantly dig a hole under my brain coral, which it called "home", even after I kept trying to evict it by filling the hole back up or moving the brain's location.
Unfortunately, I can't tell you if the dust cloud it would kick up ever got better as the days went on. My goby decided to go explore the world outside the realm of the tank one evening. Sadly, I discovered it's dried up remains the following morning.
Originally Posted by dizzyliz
Should I make sure that my rock is touching the bottom glass of the tank so the rock doesn't fall down on him?
Absolutely! Of course, just be sure there aren't any fish or critters under the rock before you push it down into the bed.