For the traditional toe the line imagery, it helps to imagine a very rebellious kid that you have firmly told to absolutely not cross some line under any circumstances.
Imagine the kid looking you dead in the eye and smirking, as they stretch out their big toe and put it all over the line while barely not crossing it.
This captures the aspect that you don't have to follow the spirit of the rules or believe in them in any way, you simply have to follow the letter of the instruction to be "toeing the line". There is an inherent malicious coloring to the term that is important, where people that only toe the line are bad people.
edit: It needs to imply that you're searching for ways to break a rule and get away with it on a technicality.
edit2: This got me curious enough to google the origin of the term, and it actually has a wikipedia article, amusingly. Apparently it has a military origin, and the article makes no mention of the negative connotations I mentioned. This makes me think my personal interpretation is actually incorrect, and I now wonder why I picked up on it. In the US, toeing the line does have a subtle negative connotation to it, and people that do it are looked down on somewhat.
They used local guides, who knew the routes, dangers and resources they might encounter.