Coding a Monthly Fee

 
I have done quite a bit of mql4 programming, and use several of my own EA on my own live accounts. But in the interest of wanting to sell these EAs to the public, how do you code in the EA the requirement for a monthly fee?
 
as soons as you make the first delivery, odds are that your EAs will be decompiled, fee requirements deleted, and spread freely in the Web.
Reason: