As a precaution, I took some clear plastic, (like couch covering plastic) and stapled it to a homemade wooden frame. There are small holes for air circulation, and I raise it for a few hours every day so it doesn't get all nasty in the bog. It isn't too terribly attractive, but so far it's kept the squirrels out.
AND the gypsy moth caterpillars, which have been dropping out of a tree in our yard like crazy.