I've heard of slot of people having this problem. I set up a chain spot to hold the dog on before the work out. New smells and wanting to mark the spot often makes one go. Heard a guy say once that he would work his on the mill a short time before emptying out. He claimed that being active made them go, which is what it sounds like yours is doing. Then we all know about using a q- tip to jump start the movement. Hope this was some help