The term 'on one's guard' is a phrase that means to be vigilant and aware of potential danger. This phrase can be broken down into three crossword solutions: WARY (4 letters), ALERT (5 letters), and LEERY (5 letters). WARY means to be cautious and watchful, ALERT means to be ready to respond quickly to danger, and LEERY means to be suspicious or distrustful. Together, these words suggest that someone is being very careful and paying close attention to their surroundings in order to protect themselves from potential harm.