Design tamper proof enclosure + detection circuitry

[Miyuki]

Wonder if I can find here somebody with experience in this field and who won't cost me an arm and leg.

This year, I will probably be designing a product, where I want physical protection against any access to the processor what is that is holding encryption keys (battery backup RAM) and doing some crypto fun.
The processor has a tamper signal input to discard data in this memory.
So I will need to have some kind of shield to activate it. It can be potted, which is probably a good thing to do.