Elevating the cage so the lizard is six feet up is the only way I can imagine that your ig can get a feeling of safety around your dog. It's the position from which parrots give themselves authority to bite their owners' ears. From that security-inducing position you can conduct anti-sensitizing introductory lessons on the floor, because they will be exceptions to the norm. No doubt your dog is much more curious about the ig than your iguana is about the dog. You might have to conduct anti-sensitizing sessions, one minute at a time, from a room away if your ig had picked up real strong fear.
Or, you can get a shock collar for the dog and press the button whenever he looks at the ig (ick). It would work though, I might do it in certain situations.
Roger