Stretchmarks are formed by the tissue under the skin growing faster than the skin itself. It is POSSIBLE for skin that is about to form one to tear if you injure a certain area because I had one pop up like that after hitting a barbell with my shoulder...but one appeared on the other shoulder in the same spot soon afterwards.
Further, if you are more concerned with stretch marks than the muscle you build, you may not be cut out for this.
Stretch marks come with the territory. Not one pro on stage is lacking them...some of them really bad like Sean Allen. That dude is nothing but stretch marks especially on his legs.
trust me, get your legs to 30" and you'll have marks all over also.