There are some general ideas to remember when ferret-proofing your home, and on the next page, you will find a ferret-proofing checklist.
If it is feasible, a good way to ferret proof is to have a single room that is completely and fully ferret-proofed, in which you can let your ferrets romp with the door shut to block access to the rest of your home. If this is not possible, you can ferret proof a larger area but try to block access to the kitchen, bathroom and laundry room, as these are areas that are harder to ferret-proof.
Make sure your ferret cannot get outside. A ferret can easily tear through a window screen, so keep windows closed at play time if your ferret can reach them. Ideally, make sure that when your ferrets are out, they cannot get to doors that lead to the outside (if someone inadvertently opens a door your ferret might dart out; at the very least lock the doors when ferrets are playing). You should also check for any small openings to the outdoors (e.g. around plumbing, the dryer vent, etc) and make sure the ferret can't get out under doors. Remeber, ferrets can sqeeze througn amazingly small spaces.
This is one of the main reasons I recommend restricting access to the kitchen and laundry room. Ferrets can easily fit under most appliances and can then get up into the workings of the appliance, which can be dangerous if the appliance is turned on or if the ferret finds access to electrical wires. Additionally, ferrets are very attracted to baskets of laundry, and could inadvertently be put in the washer (or dryer) with a basket of clothes. And a ferret that makes his or her way into the dryer vent duct now has an escape hatch! If your ferret has access to these rooms, you must find a way to block off the undersides and backs of the appliances, and you must double check the interiors of all appliances before using them or closing them.
Furniture is another favorite of ferrets for getting under and then climbing up into the inner workings. It is a good idea to tightly staple heavier fabric to the undersides of box spring mattresses and couches and chairs, as ferrets can often easily get through the flimsy fabric often used here. Recliners are very dangerous to ferrets, as the reclining mechanism can trap and severly injure a ferret hiding under the chair. Similarly, rocking chairs are a bad idea around ferrets. You also need to check couch cushions before you sit down as ferrets may burrow under or even into them. Cushions should also be checked in case the ferrets are getting into them and chewing on the foam (a danger for intestinal blockages).
Watch What they Eat
A common medical problem is blockages in the digestive system from something a ferret has swallowed, especially in kits. Ferrets will chew up and even swallow a suprising variety of items, but things like foam, styrofoam packing, soft rubber toys, neoprene, erasers, elastic bands, and rubber squeaky toys are among the most problematic. Indigestible items swallowed by ferrets can block the digestive system and require surgery to remove. You must also watch that your ferret does not ingest toxic substances, like cleaners, poisonous plants, medications, etc.