Abstract: A method of, and apparatus for, closing an opening defined at least in part by a wall which at least partially surrounds the opening. The wall has a first thickness. According to one embodiment, a strip of material includes a groove which opens in a first direction and resilient projections which extend in a second, generally opposite direction from the first direction. The method according to this embodiment includes receiving the edge of the surrounding wall in the groove. The projections project at least partway across the opening substantially to obstruct access to it. In another embodiment, a method of closing an opening defined at least in part by a wall of a cover for a valve of a fuel tank includes providing a device having a perimetrally outwardly opening groove. The device further includes resilient projections which extend generally in an opposite direction to the direction in which an adjacent region of the groove opens. The groove receives the edge of the surrounding wall.