Hi Jax, targeting the stingrays is a good way to go in your neck of the woods, not so good in Auckland as the flats are mostly too soft for safe wading and the visibility is not so good.
As a matter of interest one of the UK visitors managed to hook a big eagle ray on his 6# fly rod, it gave him a hell of a fight, I think if we tried a crab pattern we could probably hook up to rays more often, though I am not sure I would want to tangle with some of them!
All the best.
Mike