Sentence:  It must be borne in mind that huntsmen sometimes make casts which they know must lose them their fox: ... At the same time, it would be bad policy to explain these little matters: some parties, who are not sufficiently acquainted with the management of hounds, might be discontented, whereas by such a <WSD>"ruse</WSD>" no offence is given, as nine-tenths of the Field are not aware that it is not the most likely cast to recover the scent. 
Meaning of the word marked with <WSD> tags:  An action intended to deceive; a trick.