Effective input protection relies on an understanding of the source and characteristics of the transient.
Fundamentally, you need to make a voltage divider that will reduce the transient to a safe level without significantly distorting your readings. So you need to make the impedance of the transient higher, and the impedance of the protected device lower.
So put a resistor or a choke (or both) in series, and a capacitor to ground at your input pin.
There is a discussion about input protection here
We will look forward to that.