Go to YouTube and google "shooting docks"; there are good tips there along with techniques and tackle reccomendations. I've tried with a short (5ft) rod with a fast tip and 2 lb test line. So far, I suck at shooting, but my best efforts to get something under a dock is to back off the dock and throw a 1/24 oz jig with a Bobby Garland's body. I aim for the jig to impact at the water right under the door or dock and you can usually get them back 5-8 feet with a 7 ft Rapala Crappie rod.
Good luck in the shooting, it requires some patience.