ToolUIAnchor.cs

using UnityEngine;
using System.Collections;

public class ToolUIAnchor : MonoBehaviour {

    public static ToolUIAnchor instance { private set; get; }

    public void OnEnable()
    {
        if (instance != null) {
            throw(new System.Exception ("Error: Cannot create more than one instance of ToolUIAnchor!"));
        }
        instance = this;
    }
    public void OnDisable()
    {
        if( this == instance )
        {
            instance = null;
        }
    }
}