There is a website that you can buy a simple leather, patent leather, or colored leather figure eight strap that goes either over the toe and over the top of the foot and lock behind the ankle, or over the foot, then lock under the shoe. The website is as follows:
http://www.pleasureparadox.com/Kevin5/K5-SL0000.htm
I plan to buy a pair of these in black patent leather to go with the recently purchased black patent ballet boots from Amazon.com. I am slightly disappointed with them though, as I found out after purchasing them that the lock on these boots is just for show. The locking side of the strap is sewn to the boot and the other side Velcros, so there is no actual locking strap on these heels. That is ok though, because I am buying these shoe locks in a few days. My wife has the shoes at home, sent me a few pictures of them on her feet, but I am not sure if I can post pictures as of yet. I will post them as soon as I can and Will post some of me walking in them when I get back home.