I make my own kilts and just put on belt loops, no buckles.

I find that - despite losing 12 inches off my waist in the last couple of years the pressure of the belt is enough to reduce it further.

I have one belt loop on the right of the upper apron, reinforced as it gets more wear than the others as it is threaded every time I put on the kilt.

I just fold the aprons over, fasten the belt, then take hold of the edges of the waist band and pull the aprons sideways until the folds are smoothed out and the kilt lies properly under the belt.

When the under apron starts to slide down I know I have to fasten the belt tighter - though sometimes I have used a safety pin to secure it with some belts which have the holes fairly widely spaced so one hole tighter is a bit too tight for a week or so.

Maybe when I lose another 6 inches or so and have to remake all my kilts yet again I will need to put on buckes or other fastenings as my waist will not be so compressible. I am sure there are muscles in their somewhere, I can pull on them and the belt is loose - however doing that and breathing seems to be mutually exclusive....