Yeah. If so... You should saddle/spray him in the arena. When he lies down, immediately lunge him to a canter. Make him work really hard. I once had a gelding that laid down when I was riding him. Its because he was sweaty and wanted to roll. I immediately kicked/clucked/spanked to get him running and ran him a few laps. He learned that he did less work if he just stood there :P
I got summer hating on me cause I'm hotter than the sun. Win-ter hating on me cause I'm colder than ya'll. I'm being hated by the seasons so forget ya'll who hating for no reason!