when things get sloppy, ride him out foreward. Too much work on bending and flexing and nitpicking on his mouth will kill his forward. Ride out on a loose rein and let him just GO! This will freshen him.
I tried that yesterday but to no avail. I will try again. He seemed bothered by something near the barn so I tried approach and retreat, got him as close as I thought I could while just a bit out of his comfort zone but not too close so that he throws a fit and quit our ride there. It did drop several degrees while riding so maybe the weather hindered us too.