When South African Dr. Sonnet Ehlers once heard from a patient, a rape victim, that she had wished she had teeth down there, an idea was born. Read the full story here.
The product that Ehlers developed is called Rape-aXe. A woman inserts it and if she then is penetrated, the thing lodges painfully on the penis and can only be removed by a physician.
Of course, the violating act still takes place and that will still be traumatical. However, it might give a grim sort of satisfactory idea that the brute will instantly suffer from his act too.
On the other hand, it might also enrage the rapist even further which might have more nasty consequences.
Suppose that they would catch on and women would be wearing those so often that the average rapist would encounter them regularly, that might deter the average rapist. But I doubt there is an average rapist, and I think few rapes take place when a woman “expects” it.
Apart from those considerations and the other ones mentioned in the article, I can stil imagine how Dr. Ehlers got so gripped by the idea that she sold her house and car in order to get it developed.