For this kind of defensive situation you will be well served by the ability to detect, observe and accurately engage enemy at the longest range possible by day and night.
This is easily said, but would take throwing money at it to get all the equipment you need to best do it.
In terms of firearms, I would recommend tactical type high capacity magazine rifles for the main work, backed up by handguns and pump action 12 gauge shotguns. The shotguns are good for close work and if the enemy gets in to the building, last ditch stuff.
Long range hunting type rifles are good for observation (scope) and longer distance engagement. You would be best served with good optics for your weapons and also observation devices such as binoculars.
Think about night vision and even thermal imaging if you can afford it. You will also have to consider that even if you can afford a night vision device, it will only work for whoever has it so how will the rest engage? What type and configuration of these night vision devices, on weapons as sights or not?
Without night sights you can fire at muzzle flash or use whatever illumination is available, white light or whatever. A good option is to have parachute illumination flares.
Loose barking dogs on your property are perhaps the best low budget early warning system; however consider that they may give away your position if you are trying to be totally covert.
Decide on your priorities and strategy and tie that in with what money you have to spend on equipment. You can get expensive systems such as ground sensors, lights and alarms, but these cost money and you have to consider their use in a long term grid down situation.
I would prefer to spend money on optics and night observation devices which will last without grid power (but will require batteries) and can also be taken with you if you have to move locations. Here are some basic suggestions for equipment to augment such a defense:
· Appropriate tactical firearms & ammunition
· Web gear and magazines
· Ear and eye protection
· Body armor and helmets, NIJ level IIIa or Level IV
· Barbed wire, coiled (concertina) and for low wire entanglements
· Sandbags or other ballistic protection options
· Night vision devices
· Binoculars plus optical rifle sights
· Black out curtain and pre-cut plywood for windows
· Parachute illumination flares
· Trauma medical kit incl. CAT tourniquets
· Range cards
· Two way radios and/or field telephones
If you have put a group together for such a defense, they need to be trained on not only tactical shooting and basic small unit tactics and movement, but also briefed and rehearsed on the defensive plan including fighting positions and sectors of fire.
Consider that depending on your circumstances and the terrain, you may be benefited by running periodic clearance patrols around the property to mitigate against surprise attack, and to do this your team need to be able to patrol and move tactically, as well as respond to any enemy contact.
You will preferably have a medic with a trauma bag.
You do not want to ever run out of ammunition, so make sure you have as much as you can reasonably purchase. Like tactics, ammunition quantities are a subjective argument with many solutions.
I recommend a personal load of six to eight thirty round magazines on the person, with at least as many full magazines for resupply. And once you have used that, you need another resupply!
In a real life contact you will likely use less ammunition than you may during training and you must concentrate on effective accurate fire rather than simple quantity.
Train your team to engage positively identified enemy, or suppress known enemy positions. A rapid rate of fire is 30 rounds per minute; a deliberate rate is 10 rounds per minute.
Practice and rehearse the command and fire control procedures at your location, including the communication of enemy locations and actions.
Use range cards to tie in sectors for mutual support and to prevent ‘friendly fire’. Run ‘stand to’ drills like a fire drill by day and by night and be able to call out which direction the enemy threat comes from.
Be aware of diversions and demonstrations intended to distract you from the main direction of attack. Always cover all sectors, even with just one observer looking to the flanks and rear in a manpower crisis.
Keep unnecessary noise and shouting down, allowing orders and target indications to be passed around the position. Every team member is a sensor and a ‘link man’ to pass on information.
Having said all that, you are not going to open fire on just anyone coming to your location.
Any actions that you take should be justifiable as self-defense.
Do be mindful of tricks and the potential for snipers. However, don’t give up on morality and charity and don’t illegally open fire on anyone that comes near your defended location. You need to agree on rules of engagement for your sentries and you should apply escalation of force protocols to meet a threat with the proportionate and appropriate force necessary to stop that threat.
Have the ability to warn anyone approaching, whether you have permanent warning signs or something like a bullhorn that you use as part of your escalation procedures through warning to non-lethal then lethal force as you begin to identify them as posing a threat.
Remember that escalation of force is a continuum and you can bypass the early stages and go directly to lethal force if taken by surprise and faced with a lethal threat that must be stopped.