off his guard vs off your guard

off his guard and off your guard both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off his guard	No	Yes	No	No
off your guard	No	Yes	No	No

As adjectives, off his guard and off your guard are synonyms defined as:

Other synonyms of off his guard include napping, off-guard, off guard, off her guard, off one's guard.

off his guard (adjective)	off your guard (adjective)
not prepared or vigilant	not prepared or vigilant