What do you want the structure for?
I place structure in ponds literally year round, for all kinds of reasons: spawning habitat, protect yoy fish, summer fishing reefs, ice fishing reefs, bass fishing reefs, catfish noodling, bluegill condos, feeding areas, etc. There are tons of products on the market and even more stuff readily available on your property or in your neighborhood.
Let me know what you want the structure to do, and I can give you some suggestions. Also a sketch, information and description of your pond(s) would help out greatly.
