Well-draining, slightly acidic soil is the most ideal for holly bushes. Soil high in clay content tends to not be well draining so that could be one reason why your holly is not thriving.
The rust on your holly bush could actually be leaf spot or it could even be leaf scorch. If it's leaf spot, this article will help you:
If it's leaf scorch, this article will help you:
If it is indeed rust, this article will help you:
For information on how to treat rust fungus, please visit the following link:
For a refresher on the care of holly bushes, go here: