How to prevent pizza dough from stretching back
Funny enough I was until recently working under a certified pizzaiolo. Are you allowing it to rest properly? How long are you kneading it for? What is your method for shaping your dough?

Edited to add from a later comment (I don't really see the point, it's right there after all):

Pizza dough, particularly if you are using proper 00 flour, needs a solid ten minutes of kneading before it rests. Resting time will vary depending on temperature and so on, but 2 hours seems excessive to me. Don't ever use a rolling pin to shape pizza dough; you've spent all that time working air into the dough, why squeeze it all out? Shape by hand, pulling towards you with your left while pushing away in a windshield wiper motion with your right and rotating the dough slightly on each pass.