In this month's Aquarium Fish magazine the majority of the issue is dedicated to ponds. In it they have a section on making a saltwater pond big enough to house black tip reef sharks as well as nurse sharks and the smaller speceis of wobblegongs and cat sharks. I didn't pick up the issue but I am sure it would make interesting reading. I have always dreamed of turning a large swimming pool into a shark tank (ala James Bond). That would be too cool.