Almost all my fetters are available with a choice of screw fastening, snap-lock, or rings for your own padlocks, offering a range of alternatives for elegance and security. The standard screw fastening is simple, efficient and secure enough for most purposes. The device can be closed by twisting the grub-screw into the socket with fingers, but to make it really secure, just turn the screw down flush (using a screwdriver or the tool provided) and it cannot be released with bare hands.
The snap-locks in "turn-key" or "push-key" style are my own design, simple as can be with one moving part. They click shut and need either a bit of stiff wire or a very basic L-shaped key to release - enough that the wearer can't remove them with bare hands, but no risk of anything unreplaceable getting lost. If one should jam - none of them ever have - you can break into the back of it and force it with a screwdriver.
But if you prefer to take charge of your security, everything can be supplied instead with rings for your own padlocks.