Depends on what level of copy protection we are talking about :

1. If its just a security against curious guys who would like to do see what you did and maybe copy it and do not have large resources to resort to exotic means beyond a simple programmer, then just setting the lock bits on a MCU that has Flash code memory would do.

2. If you are against somebody who can afford and will go any length to do the copying, then I dont think that can be prevented.

But you are the best judge to decide what kind of risk your code is in and still feel vulnerable then resorting to copyright protection may atleast provide a legal fencing. ( And with a good attorney that fence is as good as not being there... !)

Is your code safe still ?

Raghu