I am very curious about the pond with LMB that are reproducing that also has a self sustaining FHM population. I guess if LMB are not over populated and the pond has extensive shallow weedy areas, it is possible.

I doubt adding spawning areas would lead to this.

If you enjoy doing it, do it. In the end, pond management is about enjoying it. If you are not enjoying being a pond owner, by be one?
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Men and fish are alike. They both get into trouble when they open their mouths.