Perhaps you are thinking of the phrase "I have two strings to my bow" or "I have another string to my bow." "Bow" here means part of a bow and arrow, pronounced with a long "o," "bo."
"I have two strings to my bow" means "I have another option. If one string breaks, I have another string I can use."
For example: "I'm a software engineer but I'm taking a course in firmware." "Good idea, that's another string to your bow."