The idea behind this document is NOT to impart some amazingly great design for an astral home defense system. Obviously anything of any great complexity or of personal use by myself or anyone I know is not going to be found online. (Only an idiot would openly tell the whole world the methods he uses for his personal protection.) This information constitutes some of the first material I was taught, and is being displayed here as an example of a very general design from which to draw ideas. I've stripped everything down to its basics in a mostly non-ritualistic format.
1. Select the place - a Bedroom is a good place to construct a defense system, since quite a few minor spiritual disturbances can occur when one is sleeping (sleep being a more receptive state of consciousness).
2. Do a thorough preliminary banishing of the room to remove any residual negativity or unwanted thought-forms. You can use the Lesser Ritual of the Pentagram if no other banishings are known to you. Quality protective incense is also good for changing the energy atmosphere of the room. (Frankincense was always one of my personal favorites. Don't waste your money on anything of low quality. The cheap stuff just smells bad and can make the atmosphere even worse and the air hard to breath.)
3. Charge each wall, the ceiling, and the floor of the room with each type of Elemental Energy. Make sure you're using each phase/type of energy in accordance with its characteristics. (See document on Elemental Energy). When you're using Elemental Earth, for example, you should be spraying down each wall/ceiling/floor with it with the INTENT to create strong impenetrable force fields or psychic barriers. Spray each wall down after powering up with each type/phase of energy. Visualize this strongly. You may use your breath for focus and direction of energy.
Don't use only your own personal energy or 'chi' unless you want to deplete your auric fields and make yourself more susceptible to illness and spiritual disturbances.
4. Create astral structures such as guns, walls of fire, missiles, etc. and add them as parts of your defense system in any way you wish. It's a good idea to treat a defense system (and any other type of astral structure) almost like a stationary construct. The basic methods for creating either are essentially the same.
5. For additional enhancement, you can place protective herbs in the 4 corners of the room according to your knowledge of such things. Placing and charging protective symbols on each wall isn't a bad thing to do either. (I recommend pentagrams and hexagrams.) Some people go so far as to imagine that there are 4 support pillars in each corner of the room, but this isn't necessary for effectiveness. Be creative and use whatever feels right for you.
6. You may need to periodically recharge the force fields of your defense system in order to keep it strong. Some people find ways around this by attempting to make it autonomous by programming it to draw energy from various power sources, but the average person often isn't quite skillful enough to create something that effective on his/her first try. The creation of astral structures is a skill like anything else, and it takes time to become proficient.
7. Believe in the effectiveness of the structure you've created. The more work you put into it, the stronger it'll be. Be CREATIVE and PRACTICAL and you'll come up with your own personal designs that work for you. Don't build anything the system doesn't need or that serves no useful purpose - 'just because it looks cool' is NOT a good enough reason to add something if it cannot carry out a useful function in an effective and efficient manner. A poor design that isn't well thought out can limit you more than it helps you.
Generally, it's best to create defense systems that don't advertise 'warlike' vibes if at all possible. Such systems defend by creating and maintaining a positive environment, rather than being openly defensive. (Like-attracts-like.)