It was a distilled example but realistically what I need is for the interface and parameters to be visible and the rest of the implementation to be inaccessible. This is for development of a course assignment where students will create test benches to identify buggy designs, but students should only be accessing the interface and not trying to access variables (i.e. blackbox testing). The students get the output of the testbench, but not the implementation. My current solution is to replace all of the variables in the DUT with random strings to prevent guessing the variable names, but it would be cleaner and more secure if it was just a compiler error.