Donnie,
Your skills aren't the problem. It is very possible that the 10 to 18 inch fish were pre-conditioned by fishing pressure to avoid artificials. Presumably they were caught at least once when transplanted to your pond. In my experience, when raising LMB from the fingerling size, "catchability" on artificials falls off dramatically with age and exposure to artificials. As your LMB reproduce, you should catch the youngsters, but as they age they also will likely become conditioned, whether you practice catch and release or not.
I haven't found any definitive answer to this problem, other than carefully managing fishing pressure. If you do have poachers, even well meaning catch and release poachers, they can greatly compound the management problem.
To test my conditioning theory, try fishing with a small live BG...I'm betting you will get lots of LMB action. If not, then they probably have been removed.
