Don't think of it as Obfuscation, think product activation.

Essentially the same problem. Your program contains checks à la is_product_activated(). And you don't want the end-user to use your product when it is not "activated". As a minor variant, the "activation" allows decrypting encrypted code needed for advanced features.

Did you know that perl can load and run an arbitary script whenever it is started (search for "sitecustomize.pl" in perlrun)? So monkeypatching those functions should be quite easy. And of course, there is B::Deparse, making all obfuscation futile. Decrypting the encrypted code can be done using the required decryption functions of the program, e.g. from sitecustomize.pl. The code can then be written to a plain file, using a simple print if it is eval""uated, or using B::Deparse for more complex setups.

Product activation is just nonsense. Look at Microsoft's current products. You are told that you have to activate them, but that's not true. People found various ways to circumvent the need for activation. One old and trivial way is to set the clock to the far future, install the product, turn the clock back, and enjoy a decades long evaluation phase. Another way is to fool the product into thinking it runs on an OEM system, where the activation is not needed. And you can bet that Microsoft invested a lot of work into the product activation.

Hire a good lawyer, make him write a good contract for selling your product. Sell support and updates for your product, not just the product.

Alexander