Letting out more line also helps squeeze a bit more depth from a lure, but again there's a limit. Letting out too much line actually has the reverse effect, producing a bow in the line that creates drag and reduces the maximum running depth. A faster troll or retrieve will get the lure to its maximum depth faster. Action can be an important consideration. If one action isn't working, try a lure that has a different look.
Color can make a difference.
Water clarity and light conditions will dictate which color or color combinations are most visible to the fish. Always experiment with colors. Silver and gold-finished lures seem to work well in clear water. Red and white is another good clear-water combination. These are just guidelines, however.