I have a selection of iPad sleeves on my Etsy store and recently decided to add loops and a button to them to make them a bit more secure. Here is the outcome. In some cases it is an elastic or cotton loop, in other cases it is a suede strap that winds around the button. So far, all the buttons I have used have been made from carved shells and they work really nicely with the rich obi fabrics.
You can find them on my Etsy store here.
Look out for more iPad sleeves appearing in my store soon!