I made a dirthole on the bank at the end of a old beaver dam where fox were crossing, and ran a drowner out in deep water off of the dam. The drowner wasn't necessary but there was some people activity in that area so I wanted to put the catch down out of site. On the drowner, the dirthole set location basically was remakeable several times for me, and that old beaver dam crossing took 2 coon and 2 fox for me before I had to pull up for the season. I have heard of the set you mention but have seen many variations of sets called this for fox. Just thought I'd share one that worked for me anyway.
Also, after a hard freeze, I noticed that fox and coyote tracks were everywhere on the little streams where I trapped coon earlier in the season, and the tracks went up to every old pocket set I had dug into the banks and the fox and coyotes were digging out the old fish bait and coon lure.
I chopped shallow beds in the ice and laid a piece of clear plastic wrap in the bed, then a layer of white plastic bb's, and bedded a trap in this. for an ancher wired my chains off to a 4' long thick branch and slid this into a hole in the ice so that the branch was completely under ice and could not be pulled back up. I only caught one fox for my efforts, which was a lot now that I think about it, but I always remember seeing those old pocket sets visited and wish I had a better way to nab the late season predators at those same set locations.
Jim