I'd just run on the assumption that any design you have manufactured by anyone in China can be copied. If you're really concerned, have the assembly done locally instead of by them.
But at the end of the day, reverse engineering a PCB is just a matter of time and effort, not difficulty. If someone really wants your designs, they can just buy your product and run the board through a 3d x-ray machine and/or manually map the connections. You can't patent a PCB design, and copyright is easy to get around with minor changes to the design.