don't let your guard down; carelessness is the great enemy; danger comes soonest when it is despised
be on your guard!; take care!
one must constantly be on one's guard with ...; one cannot be too careful of ...
treacherous; dangerous; untrustworthy; sneaky; cunning
alertly; vigilantly; warily; diligently; attentively
be on your guard!; take care!