First, I have to say. There is a reason this Proxy thing, despite its seeming usefulness, is not highlighted enough on the Internet.
You cannot use it to watch a random property of a random class/instance. You are only allowed to use this technique by subclassing the Proxy class.
Some operations do not expect exceptions so you need to completely understand what are you doing and why are you doing it, and your code must be absolutely clean and error-less.