Data warehouse collects and integrates critical data of organization from multiple sources and stores them for a long time in multidimensional model. This nature motivates researchers to propose set of models to secure these data. In this paper, the authors present an enhanced authorization model in order to close open security holes in Data Warehouse (DW) and On-Line Analytical Process (OLAP). They focus on adding much flexibility to formats of security rules besides controlling access to combination of fact and dimension to grant user the required permissions to perform his work only. As an integral part of this model, they present new methodology to avoid bad security impacts which are result from using Slowly Changing Dimension (SCD) techniques which track time-variant dimension modifications.