Wendy once bubbled...
Are you putting them on yur primary and backup regs? The reason I ask is that I dive with a buddy that has a secure and I can't breathe from her reg with teh secure on it when we do OOA drills. Her jaw is longer than mine and her mouth piece won't fit my mouth, its a terrible experience for me ...snip
Wendy,
The length thing is easy to solve. Lots of people get a gag reflex from the standard Secure mouthpiece.
Simply trim the rear portion of the mouthpiece off until it does not bother you or your buddy. I always had to trim my sports mouthpieces too .... not good to be barfing in the huddle at the 50 yard line.
I've found that most peoples teeth and mouths are close enough so if trimmed properly, the Secures seal up nicely. Like Rich said, a little bit of trimming works for most.