Hallo Josh,
Clamping to vdc and gnd with one diode each(e.g. 1N4148) seems to be a good idea.
In addition i would add a resistor (10K or sth like this) between the diodes an the port to limit the input-current.
Looks like this:
+
_
--| /
| ---- |
---| R |---|---------o input
| ---- |
| -
/
|
---

Michael