Web Based Indoctrination

This can be done in several ways, but none of them are really fool proof.

The easiest way would be to check the referer in http-header. This can easily be done with PHP using the $_REQUEST variable for instance. (The referer contains what url the user came from..)

Cookies would be another way to set "checkpoints", but relying on cookies is never really a good idea since they might get filtered somewhere on the way.

(Referers are sometimes filtered too by ad-blocking/privacy proxies..)

The more "secure" way to do it would be to use a Session cookie (with a unique identifier) and store the visitors progress/history in a database to check against on each page load.

The two first one is somewhat easy [if you know http] to circumvent, the cookie solution is probably easiest and the last one is definately a bit tricky.