Ive been ferreting for 20 years and have never bolted a fox...... but i do believe people do bolt them with their ferts. I have bolted mink, cats, rats, mice, stoats and the strangest thing of all a grass snake.... I was ferreting next to an old dung heap early one spring and i entered the fert in one hole and 2 seconds later out slithered this snake... I must admit it made me jump