Literally,
"the rock"
so you could use anthing variation of Rock (such as Pebble, to keep it a P name.)
Or,
Pete
Petey
Or funny nicknames,
P-body
Pete-ster
P-mento
lol that's all i got :]
Peter Alfonso goes by Peter.
Peter Clines goes by Peter Props.
Peter Pocklington goes by Peter Puck.
Peter Zadek went by Peter Arsch.
Peter Zhmutski goes by Peter Z.
Peter Siragusa goes by Goose, and Peter Goose.
Peter Cavnoudias goes by Panagiotis Peter Dias.
Peter Segal goes by Pete.
Peter Senos goes by Pete.
Peter Troast goes by Pete.
Peter Turgeon went by Bunny.
Peter Turo goes by Peach.