How to add security to your Product
If your board size and thermal requirements allow this you can use a potting compound to encapsulate the PCB.



You wouldn't like being assigned to remove that staff and whoever does try will have to put some really serious effort and I still doubt he will be able to remove it and furthermore identify the components used.

http://www.echeloninc.com/Resins.htm

Another idea of similar nature is to fill the box with Polyurethane foam, that stuff sticks as heel and no one will be able to identify any of the components even if he manages to remove it.