Help for action script game.

I am creating a game that a sheep need to jump or crouch to avoid obstacles. I had create 2 types of obstacles but they come in a constant speed. Sometimes the 2 obstacles come together make it impossible to avoid. Is there any way to change this? Can I make the 2 obstacles come in randomly in a random speed?Here is my code.

hole_mc.visible =false;
bird_mc.visible =false;

playhotarea_btn.addEventListener(MouseEvent.CLICK, removeInstructionBox);

function removeInstructionBox(event:MouseEvent):void
{
  playhotarea_btn.removeEventListener(MouseEvent.CLICK, removeInstructionBox);
  instructionbox_mc.visible =false;
  instructiontext_mc.visible =false;
  playbtn_mc.visible =false;
  playbtntext_mc.visible =false;
  sheep_mc.sheepIN_mc.visible =false;
  sheep_mc.gotoAndPlay("sheepwalk");
  treebg_mc.gotoAndPlay("bgloop");
  hole_mc.visible =true;
  bird_mc.visible =true;
  timer.start();
}


hole_mc.addEventListener(Event.ENTER_FRAME, holeMove);

function holeMove(event:Event):void{
   if(hole_mc.x>=-200){
  hole_mc.x -=7;
   }else{
  hole_mc.x=1080;
  trace("hole loops");
   }
}

bird_mc.addEventListener(Event.ENTER_FRAME, birdMove);

function birdMove(event:Event):void{
   if(bird_mc.x>=-200){
  bird_mc.x -=10;
   }else{
  bird_mc.x=1080;
  trace("bird loops");
   }
}

stage.addEventListener(Event.ENTER_FRAME, hitHole);

function hitHole(event:Event):void{
   if(sheep_mc.hitTestObject(hole_mc)){
  gotoAndStop("GameOver");
  hole_mc.removeEventListener(Event.ENTER_FRAME, holeMove);
  stage.removeEventListener(Event.ENTER_FRAME, hitHole);
  bird_mc.removeEventListener(Event.ENTER_FRAME, birdMove);
  stage.removeEventListener(Event.ENTER_FRAME, hitBird);
   }
}

stage.addEventListener(Event.ENTER_FRAME, hitBird);

function hitBird(event:Event):void{
   if(sheep_mc.hitTestObject(bird_mc)){
  gotoAndStop("GameOver");
  bird_mc.removeEventListener(Event.ENTER_FRAME, birdMove);
  stage.removeEventListener(Event.ENTER_FRAME, hitBird);
  hole_mc.removeEventListener(Event.ENTER_FRAME, holeMove);
  stage.removeEventListener(Event.ENTER_FRAME, hitHole);
   }
}


var currentSecond:Number=0;
var delay:Number=1000;
var timer:Timer=newTimer(delay);

timer.addEventListener(TimerEvent.TIMER, timerEventHandler);

function timerEventHandler(event:TimerEvent):void
{
  currentSecond++;
  trace(currentSecond);
  score_txt.text =String(currentSecond +" s");
}