In sharepoint disabling a individual list item from being updated

public override void ItemAdding(SPItemEventProperties properties)
    {
        if (properties.ListItem["updating"].ToString() == "updating")
        {
            properties.Cancel = true;
            properties.ErrorMessage = "Item is currently updating, please try again later";
        }
        else
        {
            properties.ListItem["updating"] = "updating";
            this.DisableEventFiring();
            properties.ListItem.Update();
            this.EnableEventFiring();

            // do your stuff

            properties.ListItem["updating"] = "";
            this.DisableEventFiring();
            properties.ListItem.Update();
            this.EnableEventFiring();
        }
    }