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 Zhmutski goes by Peter Z.
Peter Pocklington goes by Peter Puck.
Peter Zadek went by Peter Arsch.
Peter Siragusa goes by Goose, and Peter Goose.
Peter Cavnoudias goes by Panagiotis Peter Dias.
Peter Lefevre goes by Flav.
Peter Magnotta goes by Pete.
Peter Magurean goes by Pete.
Peter Loran goes by Pete.
Peter Senos goes by Pete.