I sometimes have issues keeping my brown sugar fresh and moist. I tried the marshmallow trick once, but it turned the marshmallow into a weird, squishy mess. Maybe the marshmallow was defective.
In any case, I found this cute little guy at Bed, Bath, & Beyond last week. You soak the stone bear in water for 20 minutes and he'll keep your brown sugar fresh for up to three months (allegedly). I'll let you know how it turns out in October. But the cuteness factor is already a win.