While playing enter this code:

R1,L1,R1,L1,square,X,circle,triangle,down.

HOLY CRAP I just found this cheat out today ,when you're Brian,in the dog race track where all the rich people are, try going into the wall. You might break through and people can't see you,even at the black gaping hole!Use it wisely because if you get caught outside the wall you can't go back in the wall

Hope I Helped!!