I found out first hand about the two belt trick.
With a belted plaid, I place a small belt under
the pleats to get the plaid onto my waist. After
getting up off the ground, while everything is
hanging down, I put on my regular kilt belt over
both layers just below the small belt (which is
then hidden inside the layers.

This two belt assembly keeps everything from
moving in the course of the days activities.
The only down side to using two belts is that
with a 60 inch wide plaid, it won't go over my
head when I need to wrap in the upper half.
It does go over my shoulders easily though,
so I don't complain.

One of the nicer points of wearing a belted
plaid, is the amount you can "adjust" it.
When it is particularly cold, you can put the
belt a couple of inches higher so the lower
edge hits just below the knees. It is surprising
how much warmer your knees will be.

The only down side of a belted plaid is that
the bulk of it is unnecessary in the climate
controlled environments we occupy most
of the time, so that bulk becomes annoying.