I have not tried land mines yet. However, do they now inflict damage upon surroundings? I.e. that land mine is going to take out that barbwire? Or is leaving a block in between the trick?
O=landmine
H=barbwire
X=spike
O O O O O
>emptyrow
H H H H H
X X X X X
As so?
I have yet to see landmines do damage to the ground or other items nearby. I've always felt pretty safe they wont destroy anything but bodies.
The setup is more like this:
OHXOHXOHXOHX
HXOHXOHXOHXO
XOHXOHXOHXOH
Spikes and barb wire slow them down and stop them, and if a number of them bunch up and the landmine goes off. Otherwise, if the zed sprints across the landmines laterally, they often will set off two or more landmines and that creates a weakness in your defense screen. If you want to stagger in electric fencing, there's also a strong way to incorporate this as well like so:
OHXOHXOHXOHX
---------------------
HXOHXOHXOHXO
--------------------
XOHXOHXOHXOH
--------------------
The purpose of this is about area denial. It works well if you're in INT, PER, and AGI because most of your ranged weapons have significant reload times, and are mostly semi-auto/single shot in the early stages of the game. Zeds get caught up in your field, and you're able to for the most part be safe upon higher ground. I like to use this tactic when I have thick (sometimes double thick cement) walls on three sides (with an escape route if I need) of me and im in a raised position. Molotovs, Pipe Bombs, and ranged junk turrets assist with clean up while you focus on the tougher nasties. This is mostly designed for solo play, but it can be effective with a group and larger bases where you purposely leave a killing field open. One Caveat: Barb wire and spikes get damaged and do not last for a very long time, and you should take that into account when you place them. Once you set them, you should wait till after a horde to repair or replace them.
If you want to incorporate trenches, this helps a little, but not as much as you might think. Trenches offer a bit of camouflage to these sort of traps. A lot of zeds will sometimes just walk around ground level spikes, but more often ignore barb wire. In addition, if landmines are not within an area you think the zeds will path through, then they are wasted. When I add trenches I ask myself if I wanna go 1 or 2 deep below ground level, but never more than that. If you go too deep into the ground, sometimes the zeds will start carving through your trenches if they can't jump out, and that may undercut your base if it doesn't have a solid foundation. Sometimes they may even glitch under foundations. If you dig down 2 blocks deep trenches, you should be able to fill them with iron spikes on top with barb wire below them, and forgo mines altogether. I tend to only use trenches later in the game and only when I have access to automatics. All the climbing and jumping and bobbing and weaving are annoying AF when I have only single shot/pipe weapons and I'm trying to proper aim.