A FET can be damaged by a static charge to the gate. Puncture occurs when voltage on the
gate exceeds 20V. Even a minimal puncture can cause the device to fail a long time after
that has occurred. It is a good idea to place a resistor from the gate to the source before
building the rest of the circuitry. This will prevent damage from a floating gate either
in construction or an inadvertent disconnect. A failed FET almost always has a short from
the gate to the source. A floating gate can cause the FET to partially turn on causing
excessive heat and then failure.
So, it might be a good idea to have a pulldown resistor on each gate so if one FET is
removed or common is lost, the other one is still protected. A 1.5K resistor on each gate
would work. That program is from another project I was working on and I changed the A/D
input and output pins.