frankly kind of debris that were picked up by marshalls at Mexico, Sochi etc better be left there than collected by marshalls like that without SC protection (or VSC depending on situation).
sure nowadays you can know cars precise positioning by GPS so SC/VSC is not an absolute necessity, but in order for that:
a. better communication method between marshal posts and race control. Maybe distribution of terminal unit like tablet to every marshal post (so that marshalls can judge by themselves on site flexibly rather than top-down) preferable
b. strict and sophisticated command structure in marshalls
c. extensive and systematic training for marshalls. e.g suppose there's 15sec gap between one car and the next, but the marshalls who run to pick up the debris should be physically fit, like semi-athlete level, also have right set of judging ability. Also "chief" marshalls, who are in position to organize and give orders, need to have good experience and expertise
d. sharing expertise across circuits. setting some sort of international standard for marshall would be ideal.
e. of course drivers need to respect yellows a lot more and race control can do better in deploying SCs and enforcing rules as well as coming up with better ideas like slow zones or whatever
all of these are necessary and maybe some more. Some of those are already necessary for cases where marshalls have to travel on off track area to attend a driver who parked or crashed but often not respected at all or not exist yet (some may already exist, I know it's easier said than done). It's doable I believe, but what's for certain is that it costs money, time and all sorts of resources. Until then, just either send SC or deploy VSC (or far stricter double yellow) before and whenever marshalls need to go out on the racing track, imo.
It's always easier said than done anyway. I remember that at Suzuka marshals came out on track quickly to catch and stop a stray tyre to prevent it from going down the hill on the track on several occasions which was probably the right decision. Every corner, each case is different so there's no one fits all solution, but it should be possible to evolve things and raise standards overall.