I can't answer your question about structure and wild predators because I have never managed a pond. I'm designing and managing the construction of 2 ponds at this time and they will both get a high percentage of structure (around 20% of the bottom area). Even though I'm not one of the experts I think the logic behind balancing predation by providing cover for fish is sound. Naturally occurring ponds usually maintain fish populations and I imagine they have more structure than the average man made pond. Of course most people design their ponds to be easy to fish and have very dense fish populations. If they accomplish this wild predators naturally respond to the ample supple of easy prey.
