For my part, first I start with perch work. So, the dog places front feet on some type of perch (I actually one of their food bowls upside down, because it has nice rubber grips on the bottom!). Once they get that idea solidly, I start clicking for ANY hind end movement, and build that into a pivot - ideally in both directions on separate cues.
Now my dog at least has the idea that moving the back feet/hind end can earn rewards.
From there I go to rear foot targeting. I use something big and easy to hit - I actually JUST started this with Blossom a few hours ago. I have a wooden plank here, maybe 3-4 ft long, 12" across, and like an inch thick. The whole thing started with her running onto and then off the plank, and me marking when her back feet were still on the plank. She would freeze, and I would continue to feed her in that position, then release. Cool beans.
After a decent number of reps, she would inevitably overshoot the plank and realizing her mistake, back up to find it with her head feet. I jackpotted her and made a huuuuge fuss about it. Now I've got her consistently backing onto the plank with her hind end, but haven't named it yet.
Hope that helps. It's a pretty difficult skill, honestly, but I find it worth teaching. There are definitely lots of ways to do it and none are wrong. It's all about whatever gets your dog thinking about their behind.