on your toes
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on (one's) toes
Active, alert, and focused. Having two kids under age five sure keeps me on my toes! This attorney is known for using really deceptive and underhanded tactics, so be on your toes.
on your toesready for any eventuality.
1921 John Dos Passos Three Soldiers If he just watched out and kept on his toes, he'd be sure to get it.