How do you keep the mating nucs from being robbed out in the apiary? I assume that you need to keep several good hives to support having enought drones... so how do you protect the nucs from being robbed out?

We are in early part of the dearth here in the sandhills of NC and I want to try grafting for the first time. Then start 10 or 20 nucs to carry through to next spring