Lesson learned! Bought a 30 pony bottle.

[Schultz]

I think one dives with a pony bottle for a different reason than "my primary is free flowing", though.  Having a redundant air source in the event of a major, unanticipated problem (and let's face it, a free flow in Minnesota water shouldn't necessarily be unanticipated) is absolutely necessary IF you are diving regularly and fairly (100 feet) deep.  That redundant air source is a great back up if something completely surprising occurs.  I've had lots of free flows and I've never bled a tank.  Yeah, they're frustrating.  Yeah, the air is cold.  Yeah, I know what to do.  I've also never breathed off my pony during one of those free flows.  Relax and slowly ascend.  The free flow usually clears.  (Of course, once it clears, you go back down to join your buddies only to have it happen again.  The definition of Minnesota Diving Insanity.)  What those unanticipated problems could be, I don't know.  I do know, though, that when I have the pony with me, I have an extra measure of security and I feel safer.  And that's a good thing.

I actually use a clip and clip my pony regulator to my BCD rather than wearing it around my neck.  It's accessible and easy to pull out of the clip (I do test that ability, even if I don't breathe off it).  Bottom line on how you secure the regulator is whatever feels most comfortable to you.  Try different methods and pick the one that works.  Hope that helps.