Howdy guys! Circles work and when using flies tied on circles, remember to use a very low profile knot that cannot be bitten apart and also don't use a loop knot on the fly. Then upon any pickup with a circle hook, do not strike at all. As the fish speeds off with the fly, he will be "chewing" the strange thing in his mouth and in the process, the hook will find it's way past all the teeth, into the corner of the mouth, and hopefully stick.
Nam-fish I'm planning another trip this year up to your side of the world. Can't wait! I was going to do the delta but I had so much fun on the Kavango, I'm coming back.