Tampion.

 
It is summertime. Bear can eat indiscriminately... and poop with extreme prejudice.
As winter approaches it is time for Bear to hibernate. No more pooping for the winter.
To ensure against leakage and anal ant attacks Bear plugs his anus with a tampion.
The tampion is said to be made with mud, bedding, and other readily available materials.
The tampion allows Bear to hibernate peacefully...
Without fear of being devoured from the inside by ants.