Went ferreting yesterday and i didnt bother with the nets on the first warren as i wanted to bolt the rabbits to my whippet as it is her first season, so i put the ferret in and he kept surfacing so i kept putting him down, i knew there was something in there as the terrier was marking, so after 3 times finally to rabbits bolted, so my guess is to keep working the ferret in the warren until you are completely sure that there is nothing at home, even try putting the ferret in every hole on the warren. Works for me