The AD8606 has ESD didoes to the supplies. However, in case of input
overvoltage, it is recommended to include series resistor (page 16 of data
sheet) to limit the current to less than 5mA.
We have also seen customers use shottky diodes from the input pins to the
supplies. These diodes have to be shottky diodes that turn on faster than the
internal ESD diodes; else it defeats the purpose of having external diodes.