Alternative methods to traditional sterilization

Hey guys,

I know that some of you are already aware that early spay/neuter can cause some issues. I recently found a study that shows all forms of gonadectomy(removal of testes/ovaries) can also cause issues.

I want to do a write up on the study but I am having trouble finding alternatives to the traditional methods. So I'm looking for a form of sterilization that would leave the testes/ovaries intact, while still preventing procreation.

Any insights?