I did end up riding Cohort for a short time late on Friday, after I felt rested and it started cooling off. I lunged him a bit and then rode him at the walk and trot with lots of bending lines to keep him listening to me. He felt "sticky" – not forward – but I chalked it up to the hot day and his lack of conditioning (he had most of the last two months off after getting a stone bruise).
Yesterday evening I saddled him up again, and mounted up without lunging first. It felt like I was astride a keg of dynamite! He didn't do anything, but he was clearly tense and wasn't walking out of it. No need to take chances; I got off and fitted him with the lunge line and side-reins and put him to work that way. No problems there; his ground manners and work the lunge line are impeccable.
After a bit I got back on; ah, much better! For awhile. Then he decided he was done. I've heard this has been the sticking point in the past; Cohort has bucked when he wanted to be done and his rider insisted he was not done yet. I was determined to be the one calling the shots, but equally determined to avoid bucking. I managed to do so by keeping him moving with those bending lines, and halting only when he would do so without trying to yank the reins out of my hands.
In processing all I've learned from his owner and my own observation, I think Cohort may be ring-sour – at the tender age of five. :-/ The antidote, of course, would be keeping him out of the arena – out on trails, or at the beach. But it would be foolish to go out by myself, and the number of riding buddies available to me has diminished to maybe one possibility.
How times – and people's lives – have changed! Years ago I had friends (and friends of those friends) who could head to the beach or mountains with a little notice – and much less expense in fuel. Now one of those friends lives in Hawaii – without horses. Another moved to Montana – with horses. A third is working full-time with a disabled husband at home; she still has horses but little time and even less energy. A fourth switched from big horses to miniature horses, and stays extremely busy globe-trotting for the business she and her husband own. I now have a son, which means less time and money and more responsibilities – including the responsibility to stay safe in order to be able to raise him....