Ditto on esshup's comments; except that I leave the main or lateral tunnel exposed (uncovered) after setting the traps. Gophers always plug their tunnel-shafts to the surface - presumably to deny a snake's appetite for gopher. So, if a gopher senses fresh air or light, he’ll immediately head to the source and get it plugged.
IMO, Woodstream makes the best version of this trap-design (the narrow jaw-spread makes for easier tunnel-insertion).
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SETTING INSTRUCTIONS)
I trapped gophers in our coastal bermuda hay-pastures back in the early 70s. Mr. Gopher would sometimes shovel dirt toward the tunnel-opening, tripping the trap before being caught. I remedied that problem by removing all loose dirt from the tunnel, then pushing the trap into the hole as far as possible and then pressing downward on the trap’s frame to secure its position. A smallish hand really helped with that part. I also used chain and a rigid-wire stake to secure the trap, since a trapped gopher would sometimes barricade himself within the tunnel with dirt. When that happened, a trap-chain facilitated the extraction process - and also the occasional "termination" deed, if necessary.
Locating the burrow is the most challenging part of the task. Before digging, I use a probe to locate the main burrow - which radiates in two directions from the mound. Once located, I dig until the main tunnel is exposed in both directions. Gophers regularly travel their tunnels, and could be in either direction from the mound. So, a trap must be set in both tunnel-directions (as shown above).
These two traps are the lone survivors of 20+ gopher traps that I "ran" way back in the early 70s. I keep them stored in my truck's toolbox, and have occasionally received free meals from restaurants and free rooms from motels after trapping these pesky lawn-rodents while visiting such businesses. Usually take less than 30 minutues. Guess that makes me an "opportunist". Still, it's cheaper than calling an exterminator.