I can't change my objects depth

programming flash
1

I am fooling around with a game, and teaching myself AS2 OOP as I go. I am running into some problems though. I pass my hero class a MovieClip, the problem is that I can’t get or change the depth of the movie clip. so my tiles are ontop of it. It is very possible that I am not doing something correctly. When I try to trace the depth it outputs “undefined,” and nothing seems to happen when I swapDepths.

 
class Hero{
 public var name:String = "none";
 private var guy:MovieClip;
 private var speed:Number = 6;
 private var spacing:Number;
 
 function Hero(n:String, s:Number, obj:MovieClip){
  name = n;
  spacing = s;
  guy = obj;
 }
 
 function get _speed():Number{
  return speed;
 }
 
 function set _speed(nuSpeed:Number):Void{
  speed = nuSpeed;
 }
 
 function followMouse():Void{
  var x1 = _root._xmouse;
  var y1 = _root._ymouse;
  var x2 = guy._x;
  var y2 = guy._y;
  var delt = (y1-y2)/(x1-x2);
  var deg = Math.atan(delt)*180/Math.PI;
  if (x1>x2) {
   guy._rotation = deg;
   } else if (x1<x2) {
   guy._rotation = deg + 180;
   }
 }
 
 function keytrap():Void{
  if(Key.isDown(Key.LEFT)){
   moveit("left");
  }else if(Key.isDown(Key.RIGHT)){
   moveit("right");
  }
  if(Key.isDown(Key.UP)){
   moveit("up");
  }else if(Key.isDown(Key.DOWN)){
   moveit("down");
  }
 } 
 
 function moveit(dir:String):Void{
  if(dir=="left"){
   guy._x-=speed;
  }else if(dir=="right"){
   guy._x+=speed;
  }else if(dir=="up"){
   guy._y-=speed;
  }else if(dir=="down"){
   guy._y+=speed;
  }
 }
 
 function get _col():Number{
  return Math.ceil(guy._x/spacing);
 }
 
 function get _row():Number{
  return Math.ceil(guy._y/spacing);
 }
}

I would really appreciate any help. Thanks