Best way to preserve a class from Code Stripping

What is the best way to preserve a class from code stripping if i still want the process to run over the rest of an assembly.

I have tried putting the preserve attribute at the top of a class as well as on all its methods and property but when running a test it looks as though the class was still stripped out of the final build.

i guessing there is a way to preserve a whole class without also preserving the entire assembly, but cant find the way of doing this when having a search.

Thanks for any help