[Dennis Christian has posted in past about a technique he used with the mepps to successfully target guard rails on the sunk bridge but I never could get the hang of it so we just drift minnows over the rails.]
Here's the rail technique re-posted:
About "rail fishing" for whites: You have to use the inline spinner technique for this to work. When fishing is slow, try "rail fishing". Locate a bridge and position the boat directly over one edge of it. You will be right over one rail and the other will be about 20 ft away running parallel to it. You can fish the rail 2 ways. The most productive way is to cast the inline spinner far enough to go over the opposite rail out into the deep water. Let it go to bottom then crank it back a few turns and let it go to bottom again. Crank it in some more and when the spinner gets close enough to the rail, you can feel the drag of the line coming over the rail. Keep cranking at a medium to medium fast speed so the spinner will not hook the rail. When the spinner clears the rail, you will feel a let-up on line tension (assuming a fish didn't latch on as it came over). Immediately release and let the bait drop just this side of the rail. When it hits the bottom, take up slack and crank several times as usual. If no bite, try a 2nd crank on top of bridge. You catch the most fish on the 1st crank this side of the rail. You will also catch a lot as spinner comes over top of rail and on 2nd crank after you come over rail.
The other way to rail fish is to make medium length cast down the bridge just inside the rail you are sitting over. Just work the inline spinner technique parallel to rail and on top of bridge close to the rail all the way back to boat. All the bridges (at Lake Livingston on Old 190) have in tact rails except the 1st one east of the river channel. The rails are OK on each end of it but the middle section of bridge is out.
My family and friends have been using this to catch whites since the early eighties. When fishing is really tough, you can usually catch them this way. Good luck and feel free to ask questions if I didn't explain it well enough.