Models have shown that levels of law enforcement in Luangwa Valley, Zambia during the 1980s were not adequate to prevent illegal exploitation of black rhinos and African elephants. Theory suggests that the deterrent effect of an increase in detection rate will be larger than that of a similar increase in penalty. The most effective penalty, in economic terms would be a variable fine related to the number of illegal trophies harvested, but this may be hard to legislate effectively. Wildlife managers conserving rhinos and elephants should focus on improving detection rates rather than on requesting severe penalties with no improvements in detection.