Right, so I did a quick Google for timex ironman straps, and found this on forum:slowtwitch.com:
Timex Ironman watch band keeper fix Quote | Reply
Now on my ~4th Ironman watch – I love the functions, size, etc. but detest the wretched band “keeper”, the little rubber ring that holds the tail of the band in place. I lost two other perfectly good watches because of keeper failure, $40 watch plagued by a 2c piece of rubber!
When my 4th (and sworn LAST!) band keeper failed a week ago I finally found a cure after trying a bunch of fixes, nothing worked for long. What IS working (so far…): snip two thin (~5 mm wide) “rings” from a cast off butyl inner tube, make sure its a small diameter tube, like for a 23mm or less tire. Put both butyl rings next to each other on the band, in place of the keeper. One doesn’t work perfectly but two adjacent seem to help keep each other in place. Been working great, and cosmetically ~same as original. Needless to say, ya need the black band version to stay color coordinated.