Front bras or masks do more damage than they prevent. Invariably, dirt, grit, dust or whatever gets in between the paint surface and the underside of the bra. Then, with any movement of the bra as from wind or vibration, scratching always occurs.
Bras or masks also trap moisture and force it into the paint which, over time, eventually leads to clouding.
If you're really looking for rock chip protection, try the 3M clear sheeting material that is custom cut to fit the contours of the car. It is virtually undetectable when installed properly and easily removed. You see it alot on high-end cars like BMW's and MB's in the valley here.
NNNOOO dont do the mask thing. Even the Clear 3m ones are bad for your car because once you take it off you will see a difference in the color dept of your car. Also if you get moisture in there you will will start seing mold start forming under that clear plastic. Im talking from experience. Just leave it as is and when necessary paint your bumper over again. Its not to expensive to repaint.