One of the best ways to secure your outdoor plants to grow in a greenhouse with locked doors or in another type of shelter. One must keep in mind while growing cannabis that plants grown outdoors do have a strong aroma that can carry over short or even long distance given the right amount of wind and the right climate. Many cultivators work around this problem by growing cannabis plants that have very neutral aroma during flowering. These types of strains are listed by most seed-banks. Again you should ask about strains that have low smell levels if the odor is a concern, bu cannabis plants will always smell to some degree during flowering.
The other thing to do is to make sure that during harvest time you have harvested as quickly and as privately as possible. Standing over a small shelter putting cuttings of cannabis into a black bag is not exactly the most secure way to go about this. Some people go out to their garden with black plastic bags and drop the bag over the plant before pulling it up. This way you will not expose your crop to anyone. Some people do their harvesting at night. This is not recommended though as it can draw unwanted attention to you.
If you are growing your plant outdoors in the open without a greenhouse or shelter and are away from the general public then you may want to create a pen for your plants. A pen made from chicken wire will prevent any unwanted predators such as deer or rodents from eating your plants. Predators are a big problem with outdoor growing. We talk about pests in our Pests & Diseases pages!