Amibroker AFL Protection

I want to create a time bound (auto expiring) dll from an Amibroker formula and so that i can give time bound access to users (like 7 days, 1 months, 3 months, one year etc.)The dll should hide all the logics of the Amibroker formula in functions and the Amibroker formula will call the functions from the dll. So actual logic will be hidden from users. Then the Amibroker formula and dlls to be packed into an [login to view URL] who have done similar kind of work needs only to apply,