Most frogs will burrow if the temp or humidity is not to their liking or if feels insecure.

A half round log hide or even a small terra-cotta pot turned on its side can work wonders.
also cover the sides with some kind of background that will also help with a skittish frog.
and lessen stress.

I have also made a shelf made from a small turtle dock
I got some plastic coated neodymium magnets and made mine magnetic for ease of cleaning and flexibility
in where to place it in the enclosure.

I have even cut a hole in one for a small candy dish that is opaque. I use it to feed crickets and roaches to
my tree frogs.

I am putting together a how to on how I made them.
I will post it soon.