Actually that is true but only because of the way they walk, not depth or necessarily size. When a deer walks, he/she'll place the back hoove in the track of the front hoove. If the second print is inside the first print it is a buck as a bucks chest is wider than it's hips and the reverse for doe, a does hips are wider than it's chest. It's not fool proof but it's mostly accurate (if you can tell which was first and second).