Grumpy_Mike:
No the diode will have a forward leakage current, therefore your pin will see the voltage on the other side. You should use a zenner or rail clamping diodes and a seriese resistor to protect your pin.
This is what I have, (oops, the vertical Diode is an LED)
When the FET is ON, I have 0v at both point a and b. With the FET OFF, I have 16v at point b and 4.948 at point a.
I guess I'm not understanding forward leakage current in this instant. Is it being drawn from the Arduino when the FET is OFF?
Thanks, your always a help.