In a situation where a person is paying child support for a child from a previous marriage, and that person then chooses to remarry, the income of the new spouse will not generally be used when calculating the amount of child support paid. While the new married couple may very well be combining their incomes and living, as a household, on a higher level than before, this doesn't affect the court's calculation as to the parent's expected contribution. In other words, essentially the law states that the income of an individual will remain separate for the purposes of calculating child support, so you shouldn't have to do anything to protect your earnings.
Stepparent Contributions to Child Support
There are a number of reasons why most states will not include your income in your child's support calculation, but the main reason is purely practical: with many people of both genders paying child support in modern years, the chances are fairly high that two people who both pay child support will marry one another. If their incomes are combined and calculated in order to raise the contribution expected for each of their children, both of them are, in effect, paying out twice: once for their own child and once for the step-child.
This means that while you can keep your finances separate, such as by maintaining separate checking accounts, you do not necessarily have to do this in order to protect your income.
Exceptions to the Rule
There are, however, some limited exceptions to the rule that your income will be safe from child support. For example, if your new husband deliberately refrained from working, the court might consider your income when determining his child support. In any given situation where an exception is sought, the court would have to make the official exception and it would be based on the facts of the individual situation.
Getting Help
To understand the specific laws that apply in your state with regards to child support, it is always in your best interests to speak with a lawyer.