To simplify \(6^{-3}\) using the negative integer rule of exponents, we can use the property that states \(a^{-n} = \frac{1}{a^n}\). Therefore, we can rewrite \(6^{-3}\) as:
\[ 6^{-3} = \frac{1}{6^3} \]
Now, let's leave the answer in exponential form:
\[ \frac{1}{6^3} \]
Hence, the simplified expression of \(6^{-3}\) is:
\[ \frac{1}{6^3} \]
If we wanted to express it as a single fraction, we could also represent \(6^3\) as \(216\), but since you requested the answer in exponential form, we will keep it as:
\[ \frac{1}{6^3} \]
This is the final answer.