Also bettas are notorious for trying to squeeze into little places -- several have died trying to go through the small holes in the bottoms of teraacottoa pots.
You thus might consider closing some of the cracks with clear aquarium sealant, and possibly sand down any edges that are scratchy enough to snag pantyhose.
If it snags pantyhose it will tear fins, as I learned to my dismay in July.
But my fishy is all better now. Please learn from my mistake!