// Place defender on mouse down
    void OnMouseDown()
    {
        // Check if there is a selected defender
        if (!DefenderSelectButton.SelectedDefender)
        {
            return;
        }

        // get the selected prefab
        var prefab = DefenderSelectButton.SelectedDefender.DefenderPrefab;

        // minus the cost of prefab. If no money => return
        if (!_starManager.UseStar(prefab.GetComponent <Defender>().Cost))
        {
            return;
        }

        var defender = Instantiate(prefab, GetSpawnPosition(), Quaternion.identity) as GameObject;

        defender.transform.parent = Defender.DefenderContainer.transform;

        // Cleanup
        DefenderSelectButton.SelectedDefender = null;
    }