No. They are meant to be tied off. Ursacks that is.
When in doubt read the instructions.
USE AND CARE OF URSACK
DO
Tie the cord with a double overhand knot–tight–so that there is no opening at the top of the bag.
If food is visible, you have packed too much in.
If you can see it, a bear can get it.
Tie URSACK up to a strong branch so that it can't be crushed or stolen. Bears have been known to chew through 5 inch branches to get to food.
Always check trailhead regulations.
After securing the opening with a double overhand knot, tie URSACK to a tree branch using a figure 8 or another knot that resists clinching, so that it can be untied easily.
Keep any food item that could leak in a plastic bag inside URSACK. Even though a bear may not be able to penetrate URSACK, he may be able to crush the contents. If URSACK does get crushed, there won't be a "food reward" that can be licked from the outside.
Machine wash, no bleach line dry
DO NOT
Do not keep URSACK in camp.
URSACK must be secured to a fixed object that is a safe distance from your camp site.
Do not keep URSACK in or near your sleeping bag or tent.