I remember reading that regardless of preventative lotions and creams, that stretch marks can occur as a result of a mineral deficiency. Also, I've read that they can be genetic. I don't have any sources to back this up however, I just remember it from past readings.
As far as post stretch mark therapy, I know lasers generally don't work. They are supposed to be more effective on "fresh" stretch marks (new, pinkish) and less effective on ones that have "healed" (after they turn white). When I was having a laser tattoo session at a laser surgeons office, I asked if they could hit a couple stretch marks with the laser (different laser than for tattoo removal). I just wanted to test it, so it was a smaller one (on bicep). It didn't even lessen it.
On the other hand, I've heard the Flawless cream from NutraPlanet has yielded good results. I've tried the Java Soap, and it may work for stretch marks, but it seemed to go really fast. In the small time I used it, I didn't notice anything (however it wasn't that long).
*Note* - Keep Java Bar Soap out of the soap dish and out of water. Big 'Duh' on my part.