Originally Posted by Linds
The other thing I've had good luck with is instead of teaching to target something with their backfeet I've first taught them to go backwards up stairs via shaping it. That seems to first of all start that muscle memory of reaching back with their feet, is more of a confined space so they are limited to what they can do and helps get that idea of maybe there is something back there attached to their body.
I was going to mention backing up stairs too. It's actually really hilarious at first to watch them figure out that they have back legs.