In this day and age most koryu do not keep "secrets" or limit exposure to certain teachings because they're afraid of being publicly compromised or feel their public dissemination will somehow threaten their legendary ability to defeat all comers. Such blathering is childish nonsense. We're not sitting around in our dojo's, closing the curtains and peeking outside to make sure no one see's the "good stuff". We're just trying to responsibly preserve something in a manner worthy of those who left it to us. We agreed to certain restrictions on how this is done and accept that we are charged to maintain those restrictions.
There is an ancient building technique I have studied. It is difficult to understand how and why it functions as it does, though it is undeniably effective. The pioneer of this method in America took out a patent on it in 1895 -- although the basic method had been used for a thousand years in his home country. In doing so, he explained it was not his purpose to monopolize the use of his technique just to keep it from imitators, but to control its use to prevent poor imitations from causing the poorly understood method from falling into disrepute and thus become lost.