With the help of this forum, i was pointed in the direction of a 555 based external reset circuit.
Having spent a few hours yesterday creating another external reset shield on a protoboard, it led me to Product idea 1.
1) A simple stackable 555 reset shield...Possibly with the timing cap and control pin either left for the user to solder, or jumper selectable.
(i like the astable designs such as http://www.chrisramsay.co.uk/posts/2015 ... -heartbeat )
Product idea 2 would be my ideal.....
2) An EtherTen 2. (Upgraded EtherTen)
Based on the Uno R3 + the equivalent of the Ethernet Shield 2 (W5500 chip) + a built in external reset circuit
and really pushing things a DC-DC converter as onboard voltage reg, saving further power.
The W5500 supports standby/sleep state for low power.
The combination of the above would allow to create an extremely low powered and 100% reliable remote monitoring solution.
The Ethernet module can then sleep until data needs to be sent / retrieved and then sleep again.
Food for thought

cheers
Andrew