Unfortunately there are so many variables that have an effect on cavitation that the only sure way to determine when it will happen is experimentation.
People tend to think with models boats that cavitation is the point at which the propeller "breaks away" and looses it's grip on the water but in actual fact cavitation can occur at any time and can cause erosion of your propeller. Cavitation is actually the creation of gas bubbles on the low pressure side of the propeller blade, which can then impinge on the blade surface and slowly erode it away. Exactly the same effect can be seen in centrifugal pumps where cavitation can definately erode the impeller away.
Although the root cause is the undesirable low pressure areas when these actually occur can be determined by the propeller configuration, as in pitch, diameter, blade profile etc., as well as the speed it is turning at, the draught it is at, the hull form, the distance the propeller is from the hull etc..etc..
For model boats cavitation manifests itself when it appears to "stall" as the prop is spinning so fast and creating so much of a low pressure area that the following blade is also passing through the same low pressure area and is therefore not capable of creating lift. Your options when this happens are obviously slow down the prop or fit a prop with a smaller pitch or possibly a smaller diameter.
Unfortunately experimentation is the only way forward to ensure you get the best performance and one of the issues I discuss regarding real ships quite regularly is the fact that it doesn't matter how much power you can generate if you can't get it into the water it's no use to you!! Exactly the same applies to model boats.