A marmot stole one of my brother's boots from under the vestibule while we were in the tent once. We got it back but since then I always keep my boots in the tent when I'm not wearing them. There is also a ground dwelling squirrel in our area that will steal glasses, big fuel canisters, etc. It pays to keep everything secured when camping.

My brother was only a few inches away from the marmot when it grabbed his shoe. From close up a marmot looks pretty big. My brother screamed as loud as he could "wolverine!". We still laugh about it.

If I had to I'd cut out foot shaped closed cell foam pieces and keep them in place by pulling socks over them.