Here's why:
* Neutering involves removing the testicles. This procedure permanently removes the source of testosterone, the hormone responsible for male sexual characteristics and reproductive abilities.
* The testicles cannot be reattached. Once removed, the testicles are gone, and there's no way to reverse the surgical procedure.
* Hormone replacement therapy is not a viable option. While hormone replacement therapy can temporarily address some symptoms of low testosterone in humans, it's not a feasible solution for "unfixing" a dog.
Therefore, once a male dog is neutered, the change is permanent.