Best materials to prevent reverse engineering of PCBA components?

I have an overmolded PCBA on a cable with passive components only. Some of the components are hard to identify, but I'm still concerned about the possibility of competitors trying to reverse engineer it. What are the best materials I can put on the components to make it extremely hard (expensive, time-consuming, etc.) for anyone to get to those components in-tact? I'm concerned that standard potting materials, conformal coating materials, and epoxies would be too easy to remove with heat, chemicals, sanding, or milling. Essentially I'd like to have something that bonds so strongly to the components that trying to remove the material also destroys the components. Of course if the material is too hard on the hardness scale, or has a high thermal expansion co-efficient, then the board components might get damaged during manufacturing or during use in the field.