I've found over the years that simple is better, no need to find fixes for problems that don't exist. A parallel guide and a pin work, are simple to build, cheap, and reliable.
Give thanks for not having a tender back.
The ratchet seems like a good way to go. My plan was to install a foot pedal attached to three pins that would be held extended with springs. Press the pedal and the pins would retract. Release the pedal and the pin for the closest hole would slip into place, holding the slide.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)