Also thornbushes if you don't mind pruning them back it keeps people from looking into your windows and generally keeps most idiots away and I mean the really big thorn bushes the ones that have if you trip into it you will be in a lot of pain.
When it comes to growing thorny plants, mistletoe leaves are very sharp, and even the most PCP'd out druggie is going to have a bad time trying to climb through a mistletoe hedge to open your bedroom window.
Rosebushes on the outside of brick walls, anti nog spikes at the top of said walls
These are all good points, and I'd like to use them to start by talking about a very important thing to consider, its really the starting point for any kind of consideration regarding security. Namely,
Identifying The Threat Profile, i.e. figuring out what kind of threats your security will need to defend against when it comes to your home. If you're a known rich person, drug dealer, or other notable then its likely you have people looking out for you specifically, and should tailor your approach accordingly. Another individual threat might be a disgruntled business acquaintance, partner, etc that is know to you. These types of threats are
specific and motivated, and are distinguished in the sense that they have a specific goal in mind and will not be easily deterred, you must actively resist them. (No passive security can defeat a determined attempt over a long enough period of time.)
Fortunately, most of us will only have to worry about non-specific threats, crimes of opportunity, random bad actors, etc - think travelling gypsies, 'joggers', bands of 'urban youths', the meth junkie. These threats aren't driven and targeted, they're looking for an easy score, a little fun, or other low level criminal activity (which they may escalate to rape and murder of course). The point is, for these kinds of criminals typically any house will do, and they aren't committed to their targets. That means that, unlike the business partner or jilted lover, these guys can be influenced to choose other targets or be induced to flee with passive defenses.
This is where having
Defensive/Hostile Architecture and exterior design come in. If your home looks like a tough target for mischief, or a risky one, then these low level threats are likely to either pass by your house entirely or give up when their efforts don't immediately bear fruit. Simple things like keeping valuable ATVs and stuff locked up in sheds, and valuables out of sight through windows is a good start, if they don't know goodies are inside they may be less likely to visit. Thorny bushes, motion activated floodlights and security signs/cameras might make them think twice as well. Combine this with simple steps like reinforced strike plates and a security bar, and you've got an excellent, simple/cheap outer layer of defense that will deter the common junkie.
Of course, you must have
Defense in Depth, that is, multiple types of active and passive security in layers. If the random criminal braves the thorn bushes and fences, strides unflinchingly into the floodlights, and decides to kick the door, thats why you have the strike plate and such so he can't kick it in first try. If he's ornery and wants to spend a few minutes battering down the door, thats fine - your alarms should have awakened you (if the kicking didn't). Now your interior defenses are brought to bear, disorientating lights and sirens of your alarms deafen, blind and disorient the intruder. If he wishes to enter, he'll need to contend with that, plus your interior doors/gates (You did install a security gate, right?) - all under the threat of arriving police (if you informed them) or you (should you intend to confront him). When you do, you have the benefit of a blinding light on your weapon, earmuffs to filter the sirens, and intimate knowledge of your home's best approaches and lines of fire. The intruder, fool he was to blunder deeper into your web of defenses, dies like a wounded animal in a pen.
Criminal home invading scum deserve far worse.
