instantiate object at the edge of screen

hi guys...right at the end of project ive found a huge problem , and ...... ive build my project in 1366 * 768 and whole of my positions are in world space but in built project when resolution changes something change , and someobjects that were in borders of screen dissapear , so i used this code for my background ( this is a 2d game) to rescale it with different resolution

 var NewObjectWidth : float ;
 var OldObjectWidth : float ;
 var NewObjectHeight : float ;
 var OldObjectHeight : float ;
 function Start ()
 {
     OldObjectWidth = this.transform.localScale.x ;
     OldObjectHeight = this.transform.localScale.y ;
     NewObjectWidth = OldObjectWidth * 764 / 1368 * Screen.width / Screen.height;
     this.transform.localScale.x = NewObjectWidth ;

 }

but because the camera aspect ratio changes in other resolutions such as 800 * 600 ,the problem of disappearing still remains , so i found a solution for this that make the objects base on resolution of cam instead of making them in world , so is there any way to instantiate objects base on the camera resolution , by the way ive used this code

 var p : Vector3 = camera.ScreenToWorldPoint (Vector3 (100,100,-4));
     Instantiate(CreateInstantiate ,p , transform.rotation) ;

but it doesnt work correctly ,the z parameter of p ..... and it should be connected to camera too..... sorry it was a long questions.....thanx alot