Get line counters so you know how much line you have out and when you pick up a fish, go back to that depth. Stick with what works. If you are marking at 15, troll them at 14-15. But how do you know you are in the zone? Rebel is 100% right. Get the precision guide to trolling. It is priceless. You should have fish in a 3-4 foot column of water. Do long slow s turns. It drives them crazy! Pick up a rod every once in a while and pull forward and let it slide back slow. You will pick up fish in the turn and after the drop back.