Timing conundrum

So in my spare time (when I'm not teaching) I do timing and race control with Wild Running (https://www.wildrunning.co.uk/). This involves a mix of short races, swim runs and long ultras. 

In the past the timing split has been a bit like this -
Shorter runs - borrowed RFID (volume over line in a short space of time)
Swim Run - hired sportident (the competitors like splits)
Long runs - GPS and manual via webscorer (GPS checkpoints, manual finish)

However, I'm now helping time events where the results rely on accurate checkpoint timing and safety demands either real time tracking of checking people in and out. The later requires a lot of people (or live updating sportident gear - elusive and expensive) and can be thrown by marshals having to respond to first aid etc. The former is expensive. So I'm starting development on a new system. 

This new system will allow live checkpoint tracking, will need to be weatherproof and robust. A long battery life is a must, as is ease of use by marshals / fit and forget.

It's going to be a challenge! More info later.