This sounds ridiculous, but growing up we had some low lying ground below our house that stayed wet year round. We would take a shovel and dig through it, like digging for redworms, and we'd get them that way. Never were more than a shovel blade below the surface.
I've caught em in riffles with a minnow net. Set the net up so tight to the bottom, above the net use a long tooth rake (mine had 4 teeth bout 6" long) and dig the gravel and rocks up a lot when done lift the net, usually have a bunch of crawdad, hellgrammites and some leeches. I've heard folks putting out meat in a shallow area and catching leeches but never done it.