To keep your furniture legs from becoming damp while you steam clean your carpet, place your furniture legs in sandwich baggies. This is especially important to do if any of your furniture legs are made out of metal. This will keep your metal furniture legs from leaving a rusty stain on your carpet. Keep the baggies on your furniture legs until your carpet has dried thoroughly.

Source: http://www.cleaningtips.com/tips/house/carpet-cleaning/furniture-legs-carpet-cleaning.html