You need something strong than what was listed.  Try cable ties.  He won't
be able to undo those unless he gnaws through them.  But being flush with
the bars of the cage should make it exceedingly difficult.
 
They are cheap and can be found at any hardware store.  For a few cents
more you can get the stronger variety.  Make sure when you use them to
clip off the excess.
 
Good luck!
[Posted in FML issue 3233]