pole vent you mean....just put it away from the sub like on the sides of the box n shit, its not gonna move around in a sealed box like it would in a ported
I never had any problems with it getting into a pole vent before, but I guess worse to worse, some uber-thin cloth chickenwire-style mesh attached to the back of the motor with nothing more than duct tape would do the trick...
Get a more matted polyfill from Hobby Lobby, the kind that is not so fluffy and loose. Get the kind used in quilting and they use 3M spray adhesive to keep it in place.