Figure four traps are not too hard to balance once you get the hang of setting them, and learn to carve the sticks well enough so that they'll not only hold while setting the trap, but also fall reliably without catching.

On a side note, if I remember correctly, Les put the main support stick under the rock, and I was taught that it shouldn't be directly underneath the weight you're using to crush the prey. Not only will this make it less likely to hurt your hand if the weight falls, but also the support won't get caught under the weight if the trap fails for one reason or another. That's not to say that how Les set it was wrong or wouldn't work, but that there was a reason I was taught differently.

Of course I should mention that I had trouble setting a Figure Four before, and the diagonal stick flew up in the air and smacked me in the face! LOL

It must be noted that I believe I remember Les setting deadfalls in two different shows, and I may not be thinking about the same episode as you. One was in the Desert, and another in the Mountains unless I'm confused.

Regarding triggers and bait, I saw a Piaute Deadfall (similar to the Figure Four) set with a piece of straw (grass) with the bait on it as the trigger. It took almost no pressure at all to set off the trap so the bait only needed to be secure enough to stay where it was. Pretty much, if the piece of straw was bent even a little, in any direction, the straws integrity would be lost and the trap would be sprung.