i have a alpheus randalli and a high fin banded goby in a 11 gallon nano , and as agu says make sure the live rock you use as the base is secure, because the pistol shrimp will dig tunnels all under and round it , so you dont want it collapsing. for building material what i did was take a hammer to one piece of live rock and smash it into small pieces , no bigger than 1/2 inch and just scattered them around the tank. The pistol soon moves them about, and i have no pieces lying on the sand anymore, they've all been moved by the shrimp.
they're fascinating to watch ,especially if you an already paired up shrimp and goby