Your sub's penis has nowhere to go in this metal penis cage from the Sinner Gear collection. The cage is bent and has a metal penis plug. This prevents the wearer from getting an erection. The plug is hollow, so your sub is able to wear it all day long. The ring around the balls has two openings which you can use to attach a lock to the cage. Take the keys from your sub and you are in complete control.
It is impossible for the wearer to take off the cage without the keys.