Constitution has something called Bill of Rights which are your rights. Also, Supreme Court (Judicial branch) is there to interpret the laws. They can declare a law unconstitutional and all disputes between individual and government are settled in Supreme Court. Supreme Court's job basically is to protect people by following Constitution.
History Freak
The government envisioned by the Constitution is one of enumerated powers (see Art. I, Sec. 8 and the 10th Amendment). That means that unless the Constitution grants a power to the government, the government does not have that power. For that reason, many of the founding fathers did not believe that a Bill of Rights was necessary (the Bill of Rights was actually passed after the Constitution, at the insistence of several states). Since the founding and particularly since the Civil War the government's practical power has expanded tremendously through the interpretation of several clauses, e.g. the spending, commerce, and "necessary and proper" clauses.
The Constitution also relies on the ideas of Separation of Powers and checks and balances to limit governmental power.
MrAcademic