My advice on the kitty litter approach is "don't do it."

Last Fall, I thought I'd save my frozen frogs by using clay kitty
litter-- pure clay, pretty expensive stuff. It turns into mush in the
water, makes a cloud if you bump it at all, and the tadpoles that I
moved to it didn't want anything to do with it. I ended up pulling it
out--I think I had 3 plastic cat boxes of it. It was incredibly heavy
once full of water and again made a mess when I moved it.

I wouldn't use sand either because I don't want it getting to my
filter & UV. The less added debris the better I think.

My pond is cement over liner, so there's no burrowing there either.
But, I did a couple things differently last winter and the frog
population (unexpectedly) boomed. I have two large air stones that are
going throughout the winter to keep a hole open, but I decided to keep
a skimmer pump going off and on to keep the waterfall running after
the filter pump had been shut down for the season, in hopes of keeping
a hole in the stream between the waterfall and the main part of the
pond. I figured this would give the frogs a place to hang out, and I'd
already noticed many tadpoles up there, which was my reason for not
wanting to let the stream freeze in the first place. It worked very
well and the stream didn't freeze at all. Overflow from ice dams
wasn't an issue for me although it's something to consider. Come
Spring, the stream was full of tadpoles and shortly afterwards frogs
appeared which either overwintered there or came from the nearby
woods. The only dead frog I found was in the main part of the pond, by
the drain, whereas the year before I pulled out maybe 6 or 7 dead ones
from the stream. The plants in the stream came back earlier as well
and even water forget-me-nots which I don't think are supposed to
overwinter in NH started appearing in the stream by late spring. The
Spring water quality was much better too--much clearer. I'll be doing
the same thing again this year because it worked so well.

I'm not sure where your frogs come from, but we have woods within
200-300 yards of the pond, and I'm sure that most of ours (green frogs
mainly) come from there. I believe that many of ours over-winter in
the woods as well. I was mainly concerned about preserving the
tadpoles last year since there were so many of them. I also suspect
that if all of our frogs were wiped out, we'd get a new supply
migrating from the woods fairly quickly anyway.

As a side note, we have the largest green frog I've ever seen out
there now. I've seen it eat small fish and my daughter was horrified
to see it eat a frog that she had just rescued from our swimming pool.
It's the size of a bullfrog, but I'm quite sure it's just a huge green
"Frogzilla" that has decided frogs and fish taste better than bugs.

Anyway, I'd avoid adding "artificial muck areas" to your pond for
frogs and instead focus on keeping their (and primarily their
tadpoles') favorite spots thawed.

By the way, my frog book says that the kind of frogs that we have
hibernate "in mud and moss around ponds." (AROUND, not IN.) I had read
the same information that you had on the 'net, but I believe this book
since it's so detailed on the subject of frogs and toads. It's called
"The Frog Book." I think it makes more sense as well, at least for the
kind of frogs we have. I'm sure that their relatives are overwintering
in mud, moss and forest stuff in the woods. You may be able to just
provide an out-of-water area (a peat moss bed or something) for them
to over winter in. However, no matter how much effort you put in,
they're going to camp out where they want to anyway. I think most of
ours returned to the woods during the Fall last year. Do you know what
kind of frogs you have?

Dave