Bass found in my pond - Second question?

I posted a previous question about how the bass gets here.

Since then, we have not really solved the problem.

We decided to drain out the entire pond and remove all Bass. This is a medium sized Pond and it contains TONS of Gallons of water!!!!

We discover it was over 8 feet deep!!!!

it takes 2 days and about 18 hours until it was completely drained out.

We found LOTS of Koi mostly 3-13 Inches, Over HALF the Guppy fishes were gone. and the other fishes are there, too.

Now the Surprise Came!

There were Black Bass flapping EVERYWHERE!

Mostly 3-4 Inches. Some 13-19inch.

We counted over 300 bass.

Seems like a large number, but the professional Aquarium guy says it is still a little number.

We thoroughly cleaned the pond and used powerful Stream to wash off any eggs in the cracks, plants and etc.

To make sure there has not been any bass that was misplaced in the other fishes containers, we slowly release each fish back.

The water is crystal Clear now.

For a week now, We spotted ANOTHER Bass! We had to put on goggles and swim with all fishes. It take 3 hours until we can net out that bass. While swimming, We found few more large bass.

The professional is back and says, these bass must of been stocked or came from somewhere else. Their mouth don't have any hook holes, so they are fresh. They were inspected, and NO they are not farm raised.

Any Other Ideas?

We've spent too much money. Otherwise all koi and etc had to live in a glass tank.