Click to Move With Navmesh

I am trying to use the navmesh path finding system in order to move my units in game. but i am facing a few problems.Physics.Raycast is not accurate with navmesh. the point where the raycast hits is not where i click sometimes. my terrain is a plane. i baked the navmesh on it. also another problem i am facing is that no matter how many clicks the Navmesh.Destination is locked for some reason. i call the method ClickToMove on a derived Class in the Update Method.

 protected Ray ray;
 protected Vector3 target;
 protected RaycastHit pointHit;
 protected NavMeshAgent myAgent;

 private void Start() {
     intializeVariables ();
 }

 //TODO placeholder method.
 protected void ClickToMove() {
     if (Input.GetButtonDown("LeftClick")&&Physics.Raycast(ray,out pointHit)) {
         target = pointHit.point;
         myAgent.SetDestination(target);
         Debug.Log(myAgent.destination);
         Debug.Log(pointHit.point);
     }
 }

 protected void intializeVariables() {
     target = transform.position;
     myAgent = GetComponent<NavMeshAgent> ();
     ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 }