I notice a lot of replies here saying things like "But nets over such and such a yard would be too big." (which I agree with) or "But criminals will ignore a law stating that it is illegal to fly drones over prisons." (which, again, I agree with).
What those people are forgetting is that security is a process and not a single thing you do. The nets over anywhere practical will prevent some intrusions, the law against flying drones over prisons will allow those with the ability to do so to do things like shoot them down or fire HERF weapons at them, and so on.
Heck, the way some AC posts read here it seems that there are no prisoners in the US since I'd wager every single security measure within the prison system has, at one point, been compromised in theory if not in practice.
I would type more but I've got to put my SSH port back from a non-standard as that's pointless because a real hacker would port-scan. Then I'll uninstall fail2ban because, after all, a real hacker's not going to use the same IP address twice. Then I'll disable public key authentication because, after all, the NSA can break that. Then I'll be nice and safe with my standard-port password-only SSH server...
Edit: I happen to be in the "Just decriminalise drugs already and let prison inmates have all they want" camp.