void Update()
{
   transform.Translate(speed * Input.GetAxis("Horizontal") * Time.deltaTime, 0f, speed *
   Input.GetAxis("Vertical") * Time.deltaTime);

 transform.position = new Vector3
 (
  Mathf.Clamp(transform.position.x, bounds.xMin, bounds.xMax),
  0.5f,
  Mathf.Clamp(transform.position.z, bounds.zMin, bounds.zMax)
 );
}