Another way to secure the arms.

2 leathercuffs, and a suitable piece of pipe !

Securing the arms is not always an easy task, but here's an idea which will keep even an 'almost-Houdini locked up.

Find a suitable piece of pipe, big enough to hold both under arms, from either end. You might use a piece of drain-pipe, PVC, 150 mm Ø. (app. 6"); and as long as the masochist's arm, from the elbow to the fingertips, + a little.

( Remove any sharp edges, i.e. by sanding - or let your masochist do that ! ).

Mount a ring, at either end of the pipe.

Lock the cuffs to the rings, at either end of the pipe, and insert your partners arms, from eiher end of the pipe, upon which you tie the cuffs around your partners arms, just above the elbow...
Now your partner will not get out without assistance..!

Of course you can use this device on the back, or with the arms in front of your partner - that makes no difference !

Its also possible to make a 'tube' from i.e. leather or canvas, or whichever you like.