Camping, food and... possums

monsters bite through my tent was stealing my bread. Since this day I try to store my food out of the tent, but I don't know where and how. I tried everything and since this first aquaiantance with a possum my food was stolen and eaten by possum around ten times in the last few weeks. I tried to hang it in trees, put in on water, I store it in Zip-Locks, even double Zip-Locks, nothing is effective. They smell it everytime. And it doesn't matter what kind of food it is, they eat everything. Apples, nuts, instant-noodles, muesli, toast... What are you doing to protect your food against possums while camping in the backcountry?