As a former HS Band director with multiple trips to the UIL SMC here's what I did:

I would mark the opening form with an orange "X." I don't know why an X and orange- it just worked. Then moving forward, each set would be marked with a paint that would fade in sunlight over time and with rain. The sets would be marked with every other marcher and the set number would be small but readable. If the show had three movements, there were three different colors. By the time the season came to UIL Region the marked sets were largely gone and we spent more time in the stadium. For the situations I was in, it saved tons of time and it helped clean the drill quickly. But this was before the newer apps that students now use. If I were teaching HS Band now, Im not so sure I'd do that again, but I might depending on the situation I was in.

Your head director is wrong- it's not a crutch. Especially if you've taught them well enough to not look down but rather look for their neighbors in the form, or guide to yards lines, hashmarks, etc..