Hi Sarah

Your Forum profile says you are in East Anglia so I am going to assume that you are referring to a site in England.

In which case your starting point is Approved Document M which deals with the access to buildings.

However, AD M does not cover all possible scenarios and so you will need to consider where the drops are, how close they are to access routes and the population at risk.

As example a site might include a terraced garden and it wouldn't be the norm to put edge protection up along the full length of each terrace that might have a similar drop to that you mention - 500-800mm. BUT you might want to look at local measures at the interface between a path going up the terrace, particularly if that path was very narrow.

Numbers seem smaller when written in centimetres rather than the SI unit, millimetres!

However, for context most local authorities have an "intervention level" for when deciding on what to do with potholes in the road and that is typically set at 25 or 50 millimetres so a TENTH of the sort of drops you are describing.

May be you need to consider which of these drops can be considered to be part of the access to the buildings or immediately alongside and those which are within the broader landscaping and perhaps even designed to give a feel for the countryside where we expect some edges and drops. 

Nothing usually set in stone in the authoritative guidance but you might get some ideas from Guide to public safety on flood and coastal risk management sites - GOV.UK

Obviously written for a different audience but the principles apply.

Also remember that if you suggest some protections, these could introduce unintended new risks of their own. 

Approved Document K addresses general Protection from falling, collision and impact.

There is of course the unknown in the mix of the residents - young, elderly, infirm, disabled etc.- some of whom have specific sector guidance relative to their needs.

Most developers show the nuclear family or urban professionals in promotional materials forgetting over time children grow up and move away, the home owner ages and moves on and eventually a new owner arrives and starts a family.