My experience is that PMOS devices do not have (or have
as good) the snapback characteristic which makes NMOS
GG clamps effective. I've tried it out. What I got was ESD
"clamps" which gate-ox-ruptured, i.e. not able to even
protect themselves let alone others.
Now, you might get somewhere with a switched-gate
clamp, but conduction density is not your friend.
I do like the GG NMOS clamp (when properly tuned for
snapback in ESD, but holding voltage deterministically
greater than abs max supply rating) for its simplicity.
Perhaps you can find a way to use it, I made many
circuits with GG NMOS both on supply and signal pins
(I prefer star protection to dual ring plus core clamp).