Need Help. What are the ways that I can help my friend avoid having his kilt drop in mid-activity *again*!

I made this 54" waist (<< 54" hips) Xkilt for a friend and it dropped in the middle of a dance. He wears it at a couple of inches above the navel. He didn't notice that it was slowly slipping lower and lower until it lost traction. (Everybody laughed *with* him and he himself laughed albeit turning red a little).

Some things I know to do:
-make sure he tightens his belt sufficiently.
-maybe he should wear suspenders

Other suggestions? Thanks!