If bluegill are upstream of your nearby CC pond, they're going to end up in the CC pond at some point. A rainstorm will overflow the pond and bring them in.

If you want a forage pond, you'll be better off with a forage species that won't take over the catfish pond. FHM are an obvious choice, it won't be a problem if they get into the catfish pond and they can endure the terrible temperature/DO conditions that a tiny, shallow pond might experience.

Ponds in TX, lake place in WI, me in CA