Just keep at it - sometimes it gets worse before it gets better. And Binka's leash suggestion is a good one. If Pepper sticks his butt in the air wait him out - he will eventually go down again. Never let him win the battle.

Also sometimes you need to go back to basics. How is his down if you are right in front of him? You don't want to start moving away from him until he is 100% on his downs at a short distance. Sometimes it is a matter of inches, not feet.