arduino - what protection is required between op amp and 5v adc?

I've created this small circuit to translate voltage drop over a shunt resistor into a usable range for arduino (5v atmega32u4) adc.

This is to measure current out of and into (charging) a 12v battery on a boat. The shunt is low side (connected to Bat-). My circuit has Bat- as Ground, Vin at high side of shunt. The shunt is 75mV at 100A.

The circuit seems to work nicely (though center was ~0.8v below the expected 2.5?)

Question(s): It should probably be some form of protection in there. If I float Vin, output goes >9v and uC-pins would be unhappy. Is a zener diode enough?

Anything else that's missing? 0.1u caps on input and output?

^{simulate this circuit – Schematic created using CircuitLab}

Answer

A zener clamp will be sufficient to protect the uP A/D input.

If the measured parameter is an AC signal, capacitors would only remove DC bias. The resulting AC signal or spikes could still exceed the input ratings.