A method, computer program product, and data processing system for preventing the occurrence of undetectable dangling pointers through memory reallocation are disclosed. Allocated memory regions that are no longer needed are deallocated but are not immediately freed for reallocation, being designated as “retained.” A memory retention metric is computed as a measure of an extent of the retained memory regions in the computer's memory space. Once the memory retention metric exceeds a pre-determined threshold, some or all of the retained memory regions are freed for reuse. In this manner, improper accesses to deallocated memory regions can be detected more easily, since reuse of those regions is delayed, while at the same time excessive resource usage and heap fragmentation is avoided by only retaining deallocated regions for a limited time (determined by the threshold and retention metric chosen).