There's an excellent discussion here on how to have your checkbox on a RoR site without having a column in the database.
What I'm wondering is if I need to have such a column in the first place. It does seem common sense not to have it (if you didn't check the box, you don't get to use the app). But I also know that common sense tends to go out the window when it comes to legalities. So I'm leaning toward having it.
We are based in the US (if jurisdiction matters) in this case.
Done it for PCI compliance without saving to the database. We just had to be able to assure any auditors that it was impossible for a user to continue without ticking the checkbox. As Josh Curren points out in your link, doing client side validation is not an option.
In order to have everybody happy, you could simply log in a specific file that the checkbox was on during the form analysis.
The log would have
Being specific, that file can be shown quickly if necessary and is easier to understand compared to a code logic.