if my gameobject touhes a border then it goes to the opposite side?

Questions & Answers
1

How do i make an object (terrain) have borders and when it touches a border, then it goes to the opposite part of the world?

2

If you want to keep the object inside some rectangle, a simple way is to compare transform.position to the limits, and revert the direction of movement when some limit is found - but only the related axis: if the object touches the min x limit, for instance, revert direction in x only. The actual implementation will depend on the way you move the object, but the basic idea is:

var xMin: float = 10;
var xMax: float = 190;
var zMin: float = 10;
var zMax: float = 190;
var dirX: float = 1;
var dirZ: float = 1;
var speed: float = 4.0;

function Update(){
  var pos = transform.position;
  if (pos.x < xMin || pos.x > xMax) dirX = -dirX;
  if (pos.z < zMin || pos.z > zMax) dirZ = -dirZ;
  // move the character according to dirX and dirZ:
  transform.Translate(speed * Time.deltaTime * dirX, 0, speed * Time.deltaTime * dirZ);
}