Adjust your FD inside stop to just barely clear the chain when in the small front-big rear combo. Maybe even rub a touch. Check to make sure it still shifts quickly. This may take a few tries to get it dialed in to get the FD cage as far out as possible and still shift. Then try to be mindful that when in you biggest cogs, you have to shift gently, ie little to no pressure on the pedals. (Remember the famous incident of Andy Schleck derailing at the Tour de France, also derailing his chance to win? That is a good lesson in how not to shift.) As said above - chain guides are cheap, light and work quite well.