Don't forget about spaces under window screens and doors, plus air ducts, the mail slot, etc. Many owners use plastic safety latches on cabinets under the sink, in the bathroom, and in other places where dangerous substances are stored. Many ferrets, however, enjoy sitting on their backs and prying at these locks until they eventually get them open. Houseplants can also poison ferrets, and the animals love to dig in the dirt around them. Be sure to check through clothes hampers before you do the wash, and be certain that your ferret has no access to a clothes drier or a recliner.
Many ferrets also enjoy trash-can diving.
Ferrets are both daring and oblivious to danger, and will spend a lifetime exploring their physical capabilities. You will not only have to do everything possible to keep them out of trouble, but must be ready to carry out many rescues as well. For instance, ferrets are good climbers, but poor jumpers. They will climb to high places and then be unable to get back down. Ferret owners call it 'teleporting,' just like they do in Star Trek.