First step would probably be firing all the staff and guards, and hiring new blood.
That's a bigger deal that you might imagine. If you fire everyone in an industry, you're restricting from employment anyone with experience or proven ability in the field. Also, what justice is there in firing the able and effective staff and guards right along with the unable and ineffective? It might make sense to fire a strong fraction of underperformers and the rape-tolerant, but not
everyone.
If it remains unknown how to enforce a ban on prison rape, that subset of guards and staff who have been fighting it for years would be the best sources of enforcement ideas. They, at least, shouldn't be fired for pursuing the same goals as you.
Overall, the goal should be to use the law and it's enforcement to show a quickly, universally, and equally applied justice. Too much delay, inconsistent enforcement, and exceptions where justice is evaded are the threats that discredit the law. Anyone can certainly see how prison rape meets those criteria. The only remaining question (and it must inherently be a difficult one or the problem wouldn't exist) is "How do we fix it?"
Prisoners have very little privacy, as they tend to use every bit of it to try to fight the system. But they must have some or prison rape wouldn't happen in secret. Perhaps take that away?
One cannot harm another without having contact with them; eliminate multiple occupancy cells?
It is thought that crime is the refuge of the uneducated; perhaps provide education?
But any such ideas must keep the overall goal of justice in mind, and any of these proposals can be criticized in that light as well. Providing education as a reward for prison rape? Deny everyone privacy and company because some will use the opportunity to rape? Where's the justice in that?
It's a goal worth pursuing, but it's also a tangled problem that'll take real effort to solve. I especially like the idea of ethics classes for prisoners; education in precisely the field in which they've proven a need. But my liking the idea doesn't prove it effective either; it is only perhaps worth a try.