Why so worried ? Is the market such that you think a larger company will do that ?
GPL the code if you are going to release it (that way you can sue if they modify your driver and only ship binary), keep the design of the hardware itself a trade secret.
If you can, integrate the design as much as you can (that makes it substantially harder to copy the design).
Another thing to remember is that if you use an embedded processor to blow the 'read' fuses so that you can no longer read back what goes on in the device.
In spite of all that, any piece of hardware can be reverse engineered.
GPL the code if you are going to release it (that way you can sue if they modify your driver and only ship binary), keep the design of the hardware itself a trade secret.
If you can, integrate the design as much as you can (that makes it substantially harder to copy the design).
Another thing to remember is that if you use an embedded processor to blow the 'read' fuses so that you can no longer read back what goes on in the device.
In spite of all that, any piece of hardware can be reverse engineered.
http://www.cl.cam.ac.uk/~sps32/mcu_lock.html
I've seen a pretty nifty hack to read out programmable micro-controllers that were supposedly secure, it's only a delay tactic.
Legalese will only stop parties that are smaller than you and in a jurisdiction where they care about such things.
2) seems to be your best bet, stick some firmware on the board and have your driver talk to an 'abstract' and idealized version of your board.
Make sure you expose enough functionality for future development.