Apparatus for preventing unwanted exposure of one or more devices to one or more undesirable substances includes at least one barrier disposed between the device and the undesirable substance. At least one shield substance is provided between the barrier and the device. The shield substance is capable of permeating the barrier sufficient to preclude at least substantial permeation of the undesirable substance through the barrier from the exterior of the barrier, preventing unwanted exposure of the device to the undesirable substance.