i used to marshall at a banger track (no previous experience, or license necessary) when I was 16, I stopped when i had a close inspection of the underside of a mk 1 granada as it mounted the bank in front of me and i dived for cover, i had to retrieve my red flag from under it so i could stop the race.
Of course you have to play it safe Bright. Absolutely. I'm talking about when we're all walking off the track together at the same speed, usually as a group. There is rarely a need to be 'held' at this point; in fact it has the potential to reduce safety as has been seen by the reaction of various drivers over the years, to what they perceive as an unnecessary physical interference, occasionally resulting in a driver lashing out at an unfortunate over-helpful (as seen by the driver) guy 'just doing his job'.
Noted cosicave, but i've heard both sides have improved in learning what goes on, what improvements are asked of etc... Can only move forward.