I suggest that you try "slobber straps".
Martin Slobber Straps - Statelinetack.com
You need reins that either buckle or tie--they come in both leather and synthetic.
I even had leather reins with a long slit. You created a loop out of the slit end and ran the end of the rein through the bit's ring and threaded it through the loop--cool design. The military even used to sew their reins to the bridle so you wouldn't loose control of the horse. It WILL frighten him if you lose a rein. Sorry to be lengthy, just FYI. =D