There's a lot more to this than meets the eye! It rather depends upon the relationship between the bound table, and the secondary table. Explain a bit more, and I'm sure that a solution will be pretty straightforward.
Think about the data that your representing in the tables, and decide what the relationship is between them. Would a relationship (Primary key/foreign key) be better that writing to two places and demormalising the data? Is the data in the secondary table derived (calculated) from the first table? Go into it in a bit more details.