Most petstores sell small plastic ones that hang on the inside of the cage.Linnies are generally not at all aggressive when it comes to their nests.We are able to reach in and check them without any issues.The plastic ones i mentioned typically have a clear plastic on one end that slides up and a black cover to give them privacy.They really are perfect for these little guys.Ourselves and other breeders of linnies use these exclusively because they are so good.They even have a small cup as part of the bottom mould of the plastic to keep the eggs from rolling all over.