Getting a unique random item in a collection

gistfile1.cs

private string GetRandomRelatedViewID(string viewIDList)
{
	BaseGenericList<BrandEnsemble.Framework.RelatedItems.Components.RelatedItem> riList = BrandEnsemble.Framework.RelatedItems.RelatedItems.GetAllRelatedItems();
	riList.Filter(new string[] { "Caption" }, string.Empty, FilterOperand.NotEquals);
	BrandEnsemble.Framework.RelatedItems.Components.RelatedItem rri = riList.RandomItem();
	while (viewIDList.IndexOf(rri.ViewID) >= 0)
	{
		rri = riList.RandomItem();
	}
	return rri.ViewID;
}

// this function goes into the BaseGenericCollection
public T RandomItem()
{
	int randomRI = 0;
	Random random = new Random();
	lock (random)
	{
		randomRI = random.Next(0, this.Count - 1);
	}
	return this[randomRI];
}