A zener is often shown as a G-S clamp (perhaps more for
in-use EOS, than in-handling ESD). There ought to be a
series resistor, pin-G as said earlier. The question of where
the "ESD" damage is incurred, and what form, is important.
If you have multiple of these than a rack of catch-diodes
and a single central clamp can be more economical and
perhaps better-performing (zeners can have limited
robustness, themselves, against ampere-range ESD peak
currents).
If these are field returns en masse I'd be looking more
at EOS than ESD. Characterize the pin(s) failure threshold
(pulsed / TLP, and DC) and you'll know what it takes to
break it; send some victims out with an ESD surveyor
and follow them through their trail to see where any
such threats lie in wait, knowing what you are looking
for.