My horse stopped picking up his feet for me for some reason this past summer. I have no idea why, I guess he just decided one day that he didn't wanna do it anymore. I leaned, I petted, I poked, I tugged the hair on his fetlocks, I pinched the chestnut... nothing!
He wasn't sore, he wasn't acting up or being feisty, he just stopped. Before this incident, he was an angel about it. He would pick them up when I asked, not grabbed, but just verbally asked. So when this started, I was really puzzled.
Finally, I said that's it... If you aren't going to pick up your feet, you're going to move them. I made him back up a few steps, then tried again. If he was still stubborn, I made him walk up a few steps. I repeated this game over and over and over again. I never got angry, never yelled, just back and fourth, back and fourth. Eventually, he got the idea that he was going to dance in the aisle or pick up those footsies. I guess dancing was worse than having his feet picked. ;)
He's back to picking them up when I ask, he's such a good boy!