off one's guard vs off guard

off one's guard and off guard both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off one's guard	No	Yes	No	No
off guard	No	Yes	No	No

As adjectives, off one's guard and off guard are synonyms defined as:

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

off one's guard (adjective)	off guard (adjective)
not prepared or vigilant	not prepared or vigilant