We address the interplay of sensing performance and the choice of an erasure correcting code used for the recovery of missing data occurring in opportunistic spectrum access when there is a collision with a primary user. The main result of this paper is the existence of an optimum functioning point on the receiver operating characteristic (ROC) curve [1], in terms of efficiency of the secondary spectrum reuse. This functioning point depends on the sensing performance and on code related parameters such as the code rate and the erasure correction capability of the code. It is a trade-off between using at best the opportunities (with a small false alarm probability PFA), the number of collisions experienced (a small non detection probability PND) and the erasure correction capability of the code, characterized by its minimum distance d, whose cost is the necessary redundancy we must introduce to perform erasure correction (i.e. the code rate).