Tori, you really need to water that baby until the leaves perk up. Stand there with the hose for half an hour and soak the entire area around the plant in a 5ft. circle really deeply. Then do it again the same day. Keep doing this until the leaves start looking alive again - not drooping.
It's not only dealing with drought conditions and terrible soil it's also competing with the other trees' roots in that spot. The cold weather will slow down the other trees from drinking quite so much since they've lost their leaves now, that will help.
But you MUST re-hydrate the rhodie or it's a goner for sure. Once you have the leaves perked up again, 3 or 4 wheelbarrow loads of compost piled all around the base of the plant (not against the trunk but as a top dressing will help a lot to make the soil hold more water. The organic fibers will work their way down into the clay/rock and act like little sponges, absorbing water down there so the roots can get it before it races by and disappears.
