At the main menu on cheat mode type
In AINTFALLIN and you wont fall of
When doin a grind

Go the training warehouse and press "x" to enter. When you are inside, pick any male skater. Then pick any "mission" your heart desires. Then skate around the outside about 3 or 4 feet arond the outside. Then youll find out thaT YOURE PLAYING AS THE PRO SKATER THAT YOU PICKED. Then press start and go to skater options. Then go to "your room". Then "edit skater". Then "face" and pick one. There you go YOUR INVISIBLE.

To Unlock Travis Barker as a character the cheats section in options
Type plus44 and he will be unlocked in the secret skaters list.