When it comes down to it, if your area of expertise requires keeping your knowledge secret then you're fucked. In the end, someone younger and hungrier will always be able to meet or surpass the knowledge level you have unless you keep moving forward and your old 'secrets' will be common industry knowledge.
Just wanted to let you know that I have this paragraph printed and posted on my cube. Too few people realize that monopoly on knowledge, if such thing is even possible, is very short-lived. It's a great motivation to know that there are others who are marching forward equally as diligently as I. Cheers to that!
One good suit is worth a thousand resumes.