INPRISONBack on the water
ATWO [a blast from the past --- how did it occur to Robert to clue this answer?] Dia de San Valentin sentiment
TEAMO [I'd have gone with the cigar brand]
The three 15-letter answers are considered truisms, but...
YOUCANTWINEMALL [you really can, depending on your opponent, and Rocky Marciano won them all]
WHATSDONEISDONE [it can also be undone, like a knot, a death sentence, or a marriage]
ITSAFREECOUNTRY [right! except for taxes and seatbelt laws ...]