I have four firefish gobies in the 150gallon, and yes, they do stay suspended in the middle, clicking their dorsel fins on their half of the tank. If you want something that hovers on the rock, consider a true goby, and not a dartfish variant -- such as a clown goby (probably a green striped) if you want color.
I'd suggest the mandarin dragonette (often referred to as a goby, but is not a true goby) as the coolest fish *EVER*, but you need tons of ripe live rock for it to flourish on -- she climbs up to the top of the stack of live rock and "jumps" during the day. When the night-lights come on, she floats to the top and rides the current along the top of the water. definitely the most interesting fish -- not to mention, personally, the most gorgeous.... and let's not forget, nothing in the 150gallon tank has even touched her. She'll look at her reflection expanding her fins, and pole dorsel fin (shorter than the males, yet still long).. truly beautiful.