The more times a LMB gets it's lips ripped off by a bait, the less inclined they are to bite it again. The older the fish, the more bad experiences it's had.
Fluorocarbon line, lighter line, matching the hatch with the most realistic bait you can, and if that fails, like was said, use live bait.
How many acres is the pond, and how many pounds of LMB do you harvest every year?