IP business, How to protect FPGA configuration PROM.

I am developing IP core.

Generally, IP core price is too expensive to small company.

So I would like to sell the FPGA configuration PROM with bitstream of my IP core.

But PROM copy protection is a problem.

I want to know how to protect IP core and PROM copy.

If it is possible, I could sell the PROM with adding some royalty.

I think that this business model is good for IP core provider and IP user.