You could screw it to the mast just below the track, and swing it up to keep the slides from falling out. The price is right, and it can't get lost.
This is how I remember it being done the last time I used a boat with a wooden mast - an early 50's Lightning.
Doug
JonLee wrote:I (as many other before me) found a track stop to be outrageously expensive. Instead, I ended up getting a track slide that had a thumbscrew on it: https://www.fisheriessupply.com/race-lite-special-5-8in-sail-track-slide-with-screw-stop-348-ax. This worked just as well. To reduce the chance of losing it overboard (inconceivable!), I have it tied to a short length of spectra, which is in turn tied to a convenient spot on the tabernacle.