In this paper, we investigate the design of a truthful auction for the case when a primary spectrum owner is willing to lease its idle spectral resources in sequential time periods. The secondary cognitive radios participate in the spectrum sharing auction by declaring to the primary their types, which consist of their arrival and departure time instances and valuations. The adapted methodology aims at reducing the collusion incentive among secondary users through the proper choice of the pricing policy and replacing second-price policy, such as in Vickrey-Clarke-Groves (VCG) auctions, by the critical value auction. Furthermore, the proposed auction is dynamic and is performed on-line, in contrast to static off-line schemes such as VCG. Simulation results confirm the anti-cheating property of the proposed auction scheme.