They are pretty hard to catch short of removing all the rock. And even then, they could be hiding in a rock.
You can trap them in a portion of your tank by getting a piece of plexiglass cut to the width and height of the tank, and moving your rocks around a bit. Once you know where he's hiding, put the plexiglass in to separate him from the rest of the tank. That will make it easier, less room for him to run.
On another note, I was intrigued by your "location". So intrigued, in fact, that I had to google it. Which leads me to this question: Do you really live in Disco? If so, do you live in Disco, Texas, Disco, Illinois, Disco, Tennessee, or Disco, Wisconsin? I had no idea there were so many towns named Disco.