Replying mostly because I'm really interested in what each of you has to say about it, but I can't add much myself... I believe it's by far the most difficult thing for me to teach, and one of the reasons I don't teach English 'professionally' (only to friends and family).
I use the snorting/hand on the belly technique to show that stressing a syllable is a physical thing and that it has to do with breathing (yes, a certain Pìers Messum taught me this, as you'd have guessed).
In the past, someone showed me this with a rubber band. I had to hold each end with each of my thumb and forefinger, and pull it gently every time I had to stress a syllable. First I'd do it silently, then just humming, and finally saying the word or sentence. I'm not sure it was a very good technique, since obviously my intonation in English is still very French! It's the first time I think about it again, though, and now I'm thinking I could try it with students (as I now only work online, I'll never have the chance to try techniques physically involving several students).
Recently I played with the size of the words during an online lesson, to help two students see what I was trying to show them by humming (the humming left them clueless at first).
So, I wrote a series of simple things, like:
Tiago took a rod. He took it.
Gustavo gave you a rod. He gave it to you.
Tiago has some rods. He has some.
The blue rod is on the table, not the green one.
The blue rod is on the table, not under it.
I thought it was going to be easy for them, but it took them a lot of concentration and focus to get there.... I don't know if this will have a long term effect...
Cédric Lefebvre
Creating Within You a Mastery of French