Use the following trick to easily unlock the "Super Hammer" cheat, which requires
100 EDF kills with the sledgehammer. Go to Dust near the Chemical Depot that is 
by the Badlands. Kill a few guards, then go back out of the depot. Wait for cars
to pass by, then take them from the civilians and guerrillas. Form a wall using 
these cars with only two openings just big enough for people to fit through. Wait
for the EDF to start coming in through the holes. Take out the sledgehammer and 
hit them with it. If they start trying to bash the car wall, blow up their cars.
You can use the sledgehammer, but it will take awhile. Try using the explosives 
because the kills do not have to be all in a row. Keep doing this until you have
killed enough EDF. Note: Do not go into the Chemical Depot.