For years I've had a problem with wayward leader and tippet materials and fly lines. The leader and tippet problem is kind of solved as the tippets come with a rubber band that holds the fluoro on and the plastic housing holds the leader material inside the two halves. But my spare spools always seem to unravel especially when they bouncing around in any kind of sling pack I have on.
I came across these rod holders on Amazon, HERE. They're designed to hold together rods that have been broken down. One of the options was a set of six that were 13.8 inches in length. For $9.99 they were worth a shot.
The Amazon warehouse near me must have a ton of these on the shelves because they came the next day. A quick wrap of the line and the BOOMS velcro strap and I was in business. They fit inside the spool perfectly. They may be even big enough to fit around my big-boy 12 wt. reels when I have taken the fly off and reeled in. I have had my rods stored in my SUMO hood mount rod holders and the line finds it's way loose and then bangs all the way against the side of my truck and 195 on the ride from Deal to Titusville. There goes another hundred.