I am a little confused on the method to use for my Schutzhund tracking dog. Should I use only food drops in the footprint or a food drag?

There is not a right or wrong answer here. Both methods are legitimate forms of training a dog to track for sport. Each method has strong and weak points. For example, with a food drag (i.e. TRIPE) the dog learns that his food is always at the end of the track. So the longer the track (once this is understood) the higher in drive the dog becomes. Where as with food drops in the footprints, the longer the track the more the drive goes down.

Food on the track allows you to train in a track that is much older than the food drag method. So one has to determine what is best for that particular dog. When a dog is getting food drops - the handler needs to determine how much food the dog is to get for a day. That amount of food is divided up and put on the track and at the end of the track. So the end may only have 4 or 5 pieces of food and the rest is on the track.