I've been enjoying and learning valuable information from your books and your blog, and thought I'd share some of my expertise in hope of helping others to prepare.
If, like me, you've been slowly adding more security to your bug-in location or retreat, you've been adding perimeter defenses such as fencing, detectors, etc. in order to prevent people and/or vehicles from easily gaining access to your property. If you have more funds than I do, then you've probably installed harder defenses, such as bollards, ditches, and maybe even concertina wire. These measures will stop most vehicular threats, and oh, sure -- nothing is going to stop indirect fire (mortars, artillery) or attack from the air, but there is a much simpler way to gain access that we all need to be aware of: heavy equipment.
Having worked in construction for many years. I, like thousands of others, have acquired and collected keys to most types of heavy equipment, to include bulldozers, front end loaders, and excavators. Bottom line is, there are too many keys out there, and unlike most vehicles, most manufacturers use just one key for all their equipment, A good example is Caterpillar who for at least thirty years has used the exact same key for all their various types of earthmoving machines. This makes it all the easier for someone to "borrow" or steal one, and if TSHTF, there will be a lot of equipment sitting around at abandoned quarries and job sites.
While much as been written about the threat of gangs or other marauders using stolen APCs or other armored vehicles, it would be much easier to use heavy equipment to attack your place. Here's one scenario:
A group steals a medium sized front end loader and welds thick steel plates surrounding the cab. They fill the tires with foam (some machines already have solid-filled tires) and head for lucrative targets. Most loaders will go down the road at 25 mph, so there's no need to bother with a transport truck. They approach your perimeter...you see them coming and open fire...the machine doesn't stop because the engine is in the rear and hard to hit. Most likely, they just go right through your gate. The stoutest locks and hinges will be no match for a 15 to 20 ton behemoth. If for whatever reason your gate looks like it might be too much trouble, they will gain access at some other point. Ditches can simply be filled in, bollards can be dug out of the ground or covered with a mound of dirt, same with fences or other obstacles. So how do you stop it?
First, try shooting the tires, hopefully more than just one. There's a good chance they're not filled and will rapidly deflate. It won't get far with flat tires. If that doesn't work, try flanking it and pour as many high-powered rounds as you can into the engine compartment. Even if all you can cause is a coolant or oil leak, it won't get very far. If you have tracer rounds, you could go for the fuel tank. Most newer loaders have it under the engine, some older ones have it on the left side of the cab.
The other method is to burn it. The center of the machine has many rubber hydraulic hoses and will usually be covered in oil and grease. A few Molotov cocktails should do the trick, but consider that the machine will be accompanied by armed men on foot, who will have to be taken out first. Except for the tires, the same would apply for tracked machines.
Hope this helps. Keep prepping! - B.B.D.