USE DatabaseName
GO

CREATE TRIGGER [Table].[uPreventUpdateOops]
ON [Table].[Column]
FOR UPDATE AS
BEGIN
     DECLARE @Count int
     SET @Count = @@ROWCOUNT;

     IF @Count >= (SELECT SUM(row_count)
         FROM sys.dm_db_partition_stats
         WHERE OBJECT_ID = OBJECT_ID('Table.Column' )
         AND index_id = 1)
     BEGIN
         RAISERROR('Cannot update all rows',16,1)
         ROLLBACK TRANSACTION
         RETURN;
     END
END
GO