Sounds funny, but Wally doesn't know how to do "roll over", perhaps one of the quintessential tricks for every dog. It's not something Wally seemed to enjoy even trying, let alone starting to learn.
Then, not long ago, he started flipping partly over on his own during our daily morning play sessions. He would get all wound up and excited like he always does, and then suddenly, flip! He was on his side. So seeing this, I rewarded it with a treat immediately and started trying to coax it out of him again.
It took a while, but he started to get the idea of what I was trying to lure him to do, and when he did, I gave him a treat. Then I wanted him to get more upside down and on his back so he can get used to the feeling and how to control his body to better perform the flips.
He's getting the hang of it a lot better, and he readily will go on a flip, and even will do so on his own now if I hold out on him, like during shaping.
I do still do the luring-type actions, especially during play to continue encouraging him to work with his body overturned like that. He doesn't mind it at all and is very excited just like all the rest of the time during play! In fact, I can really mess with him and scratch him on the back of his head and he's trying to get me and just having tons of fun.
I have some pictures of the luring part of a play session.