I found out why Pie has been wanting out of the pasture even though he's only been out for a few hours to graze. One of the boarders mentioned that when she's taking her horse and Fritz out of the pasture in the morning to feed them (I've fed mine several hours earlier), that Drift starts chasing Pie, running him around the pasture in a big circle for several laps - she's seen this happen several days in a row. Drift is faster and more agile than Pie, and apparently sometimes cuts him off and then swings around and kicks out at him before chasing him some more. This is why Pie's been sometimes out of breath and sweaty when I come to get him. The odd thing is this only happens sometimes - most of the time Drift ignores Pie or is fairly friendly, sniffing noses without incident and grazing side by side. The behavior seems to only happen when someone comes to get a horse out of the pasture - at least as far as we know. One time when I got Pie out when he was panting and sweaty, Drift was standing a ways off just resting with a hind leg cocked, not looking or acting aggressive at all. This behavior is similar to what Drift did with Fritz when Fritz rejoined the herd - Drift would run him down the fence line if Fritz showed interest in the mares. But the behavior with Pie doesn't seem related to the mares - they weren't even nearby this morning - it seems to be more a matter of "herd control" - herding Pie away from the "his" geldings when they're near the gate, or "gate control" - not wanting Pie to stand near "his" gate. So far Pie's had the good sense and sufficient speed and agility to stay out of the way. I expect Drift'll settle down once Pie's been out there for a while - at least I hope so. It seems that Drift is quite the jealous, possessive type, and not just about the mares.
Pie's at a normal weight, but Drift is getting fat and Dawn looks like she's pregnant. Despite our near-drought conditions until recently and the heat wave, there's still a lot of grass out there - our acreage is quite large for the small number of horses and the pastures are profuse. The horses are staying out longer as well due to our addition of night turnout. More grass equals more calories equals fat horses. So today I brought Drift in to the large dry lot (which does have grass, just not as much as the pastures), and put Dawn in a small paddock with fairly skimpy grass. On hot days they can come inside their stalls under their fans. Of course Dawn and Drift have been out of work so that hasn't helped either. It isn't a bad idea to give Drift some "solo" time right now anyway - I hope it helps reduce his attachments.
I rode Pie this morning after I rescued him from Drift. We started by doing some in-hand work on his backing. My objective was for him to back softly - which means with his head and neck not dropped between his knees, which has been his default when backing. This backing wasn't soft, despite the curled up head and neck, lack of pressure in my hands and backwards movement - in fact his whole body was stiff, he was on the forehand and not using his hindquarters. By keeping my hands fairly high on his neck, I was able to help him find the soft spot where he relaxed his head and neck, giving at the jaw and poll, but without ducking. It took a few tries, but he got it and the back became very nice. I mounted up and we worked some more on backing - it was my job to be sure the soft spot was in the right place which also meant I had to be careful not to give him a release for ducking. By the end of our backing work, it was very nice, and as we rode I would stop and ask for back from time to time and he was consistently able to do it while using his body properly. We also worked on his softness at the walk, walk/halt transitions and softening at the halt (without backing). He did really well, and we did a bit of trotting at the end. We also did a lap around the outside of the arena, which certainly wasn't a trail ride but was the next best thing (trail riding is a bit of a worry for me since that's where I had my accident).