Answer:
they had a great standing army with weapons under the king's protection.
Step-by-step explanation:
During feudalism most nobles had direct connection with the king. They had the power and privilege to raise an army that could be either used for their own welfare or for the protection of the king.
Most nobles were also knights and commanded large fleet of armies at their discretion.
Therefore, even if the nobility were a small percentage of the population, the serfs could not revolt against them because they had a great standing army with weapons under the king's protection.