Only about 1 goblin in 100 will get past a dodge-this walkway that is 1x11. If you do 2-tile wide walkways, you should increase the length into the 15-20 range to be sure. Put some cage traps on the inner side of these walkways to catch the tricky goblins who manage to get lucky.
My surface level dodge-this walkways are filled with training weapons. On the Z level below, to the sides of each walkway, I have a parallel set of walkways where those who dodge will land and be stunned. In order to get off that level and back up to the surface, they have to cross at least 10 more tiles of dodge-this traps. Which puts them back in the middle of the upper walkway.
Repeat the above for another Z level or three below the surface. The goal is to slowly get them to dodge deeper and deeper, increasing the number of traps they have to successfully navigate to escape, while not wounding them until we get past the "catcher" levels. Note that I do *not* put traps on the "catch" walkways, I want them stunned, but alive and mostly unharmed. So I put my dodge-traps instead on the exit points of the "catcher" levels. This maximizes the number of goblins you can catch as they all try to chase their leader down the rabbit hole.
Eventually, they should either continue to fall down 1-3 levels, run back up, repeat the process, or make the final plunge to their doom and fall to the bottom of the pit (which can be anything from 5-50 levels deep).
To get out of the very bottom of the pit, if it's not insta-kill depth, they have to cross my line of really nasty masterwork traps. Which is a 2-tile wide walkway filled with as many weapons as I can cram into a trap.