It is the easiest way to see what made it through but could change their behavior if supplemental feeding is used for too long. Also keep in mind corn is not always the best to use, instead mix some soybeans and/or oats in with the corn. As far as how long a bag will last, that is up to the amount of deer that use the area. I will say as deer find the feed more will follow. The area I feed in I could dump 50 lbs a day and it would not be enough.