craftgrrl | Sewing I can handle. Bleach on the other hand...is stinky.

I'm currently slaughtering a pair of old jeans per request of my younger sister. She wishes to have a certain design bleached into the bottom foot or so of the legs.

Now, I did this to a pair of my jeans a year or so ago, but the bleach (though I diluted it) severely weakened the denim. It wasn't a month or so until it began to come apart while washing. Plus, the bleach/water mixture I used bled more than I would have liked.

Anyone have any suggestions as to how to prevent either of these things?
Wish I had a photo. Sorry.