Scott, they make magnets with plastic housing that pass right through the cow nowadays.
The nails stick to the magnet and the plastic protects the tummy.
Another thing cows like to eat in developing countries is plastic. Karin showed me some pics of a surgery her friend had performed, I think they removed enough shredded plastic to fill a 50 gallon trash bag out of a cow.
Oz, the fruit tree is a good idea.