Sanford Whiteman Its great that you have found a way to integrate Recaptcha with a bit of coding but I really think there has to be a simpler way to implement it than so much coding.
Almost all other form solutions have this functionality in place.
There is no point in purchasing an automated marketing solution and then hiring seperate Developers to code and improve on the solution
There is no simpler way, I don't know what to tell you.
In my opinion anyone purchasing Marketo should have a capable developer on call (not necessarily on staff) for this kind of spot work. It's a few hours of work max, and only a tiny bit of it is "coding".