Today I found another nice, big second year dahlia seedling was attacked even though it's planted in a 1 gallon pot sunk in the ground. Other smaller dahlia plants have gone missing, but they are not especially missed by me.
Strategy to capture the pest: I left the 1 gallon pot ( that has the gopher chewed 3-4" hole) in the ground, removed some dirt, put the Gopher Hawk in place, and then placed a seedling I've decided to cull into the hole, as "bait". The gopher will have to go past the trap to get at the dahlia. Seems like a good use for dahlias I want to cull. We'll see...
In this case I have another plant of the second year seedling( my favorite 24312) growing in a different part of the yard. The only good news is I salvaged two of the three big stalks and took small cuttings. Frustratingly, most of the cuttings I've grown under lights have just not rooted. So, I'm taking a play from @SteveM , and trying to root the cuttings outside in a shady location.