ConfuserEx is probably the best free opensource obfuscator available. Not sure can it be run on mono on linux, but it pretty surely run with wine atleast. it also has a command line tool included, so if you are planning on some automatic build obfuscation, its possible. Remember tho that you cant make your software uncrackable. you can make it harder to view the code and harder to crack, but its always possible. If you want to protect some important parts of your code, I'd recommend making a server that would communicate with the client and the server would run the important method and return its result to the client.