looking for a lasting solution against insufficiently visible side dot markers ....

[tjmicsak]

Paint markers. Use a black if you are over white binding or use white if you are over a dark binding.
The paint will dry as a dot and if you ever wish to remove them they will scrape off with a fingernail from the finish/plastic binding.

Shake them well and get the paint to the tip so all you need is a light tap of the tip to set a small round dot.

[rolijen]

Totally serious, I use a Sharpie.

Same. I’ve been doing this for many years on the edge of the fretboard on a Yacopi classical I brought back from Argentina in the 80s. The black sharpie dots fade after a few months but I just reapply. Takes 30 seconds.

[hotpepper01]

Fretboard sidedot lights? Long lasting? Yes ! Visible? Sure. But I would never recommend this at all,

[Laurence Finston]

Fretboard sidedot lights? Long lasting? Yes ! Visible? Sure. But I would never recommend this at all,

Those aren't fret markers, that's the emergency lighting system so the notes can escape in case of fire.

[sm80808]

when I was first starting playing classical as a kid my teacher used a gold paint pen. I had to reapply periodically, but it was cheap and worked. It wasn't that long before I didn't need the dots anymore.

It was something like this:

[RJVB]

How about small drops of model paint (or applied with a tiny brush), or the paint sold for small repairs to cars?