A crucial task for a network of cognitive radios is to detect occupied frequency bands, to protect transmissions of primary users, and to identify spectrum holes to maximize the utilization of wasted resources. This paper is motivated by the need to account for challenging constraints that naturally arise in such applications such as channel model uncertainties and demanding sensitivity constraints of the sensing devices. We propose false discovery rate (FDR) based cooperative strategies to sense the occupancy of the spectrum. The strategies we propose could either be used to maximize bandwidth utilization or to provide guarantees on incurred interference levels. The proposed strategies are robust to significant uncertainties such as lack of CSI, fading and shadowing effects. The key idea of the paper is that the twin objectives of bandwidth utilization and interference control can significantly benefit from group testing across all channels in contrast to conventionally employed channel-by-channel detection strategy. Furthermore, it is shown that the cooperative sensing strategy significantly reduces sensitivity requirements. We quantify the effect of channel occupancy rate on the required cooperation degree for achieving a guaranteed level of primary user protection.