To avoid stretch marks apply cocoa butter. It works for me.
Whether or not they're permanent, my best remedy would be to prevent stretch marks before they're a problem. I suggest using a lotion high in vitamin E. I'm 6 1/2 months pregnant, and don't have one single stretch mark.
Apply aloe vera gel, cod liver oil, or vitamin E oil to affected areas to help the healing process.
Eat lots of nuts and seeds and take zinc and vitamins A, C, D, E, and B-complex as a preventative measure.