Flintknapper....that must have been a pretty exciting experience with that large guy in the snare !! I have a box of snares in my garage that a friend gave me and have some trails where they should be productive. I guess maybe I will have to give them a try...
Fence crossings and trails are good places to set snares. Typically, I put a game camera on the area I plan to place a snare first. That way...I can confirm it is hogs (or mostly hogs) that are using it AND I get an idea of the size of the hog and whether or not a mature hog is in the lead or little ones. You'll want to adjust the size of your loop and height placement accordingly.
At fence crossings I will place dead limbs in a 'Vee' shape right before the snare to help direct their movement into the snare. When you consider the relatively small size of the snare loop and the fact that a hogs heads needs to go inside of it (not brush along side it) you have to be pretty precise. Deer more often jump a fence rather than go under it, but it just depends on the location. If you see fence crossings with ONLY hog tracks underneath it (and hair on the wire) then it's a pretty safe bet no extra measures are needed to avoid catching something other than the hog.
You can place objects around and over the trail if needed to discourage deer from using it. Hogs will push right through it.
I don't like to set up snares at terminal sites (water holes, bait station, bedding area). The reason for this is that when hogs approach these areas...they will generally slow down and either surveil the area of approach it with caution. We don't want that since snares work best when an animal goes through them briskly.
Under most conditions..hogs travel more quickly at night so consider where they are going at that time and set your snares in those areas.
Check snares as early the next day as conditions allow. Any hogs that have not been dispatched by the snare will definitely start pulling/fighting against it. A big hog will eventually twist or kink the cable enough to break it, even when using swivels.
And don't underestimate the power of a Feral Hog, anchor your snares to something stout.