Chris kind of hit on it. If you can get a pistol and goby to pair (best luck with the
diamond goby) the goby will only be bothered when others come NEAR his hole(s). ANd he won't do much...just try to shoo them away.
As far as them being behind rocks. They usually (or at least MINE does) dig more than one hole. And their main interest is to dig the hole(s) where they can see what's going on the most. So if most of the action is you walking past the tank, etc...then there's a really good chance they'll make their home facing that direction.
Facinating pair to have and I recommend them. But it may take a while before they find each other and pair up, so don't get discouraged early on.
Also, keep in mind, bigger pistols CAN (most often don't, but CAN) take out some of your smaller fish/hermits.