This is either an idea of pure genius, or utter stupidity. What about some company making ''Tuning Rings''? By that I mean plastic rings, of various thicknesses, so that when you have set your main tuning slide, you measure the gap, select the combination of ''Tuning Rings'' that equal that gap and then slide them on. This would then stop the slide being pushed in in error, as I often do on tenor horn when when resting the horn on my leg. They could be made for each type of instrument, horn, cornet, etc. and looking at various makes the main slides don't seem that different in size from one to the other. Genius or what?