Anyways, he is a well behaved horse, has a lot of try, loves people etc. but I've noticed that after about 45 minutes to an hour of riding, and anything past that (and less on a hot day, for instance I rode him in approximately 85-90 degree weather today for 30 minutes) his attention span is gone, it's almost like he shorts out and doesn't want to walk, very very unsure suddenly and just seems like he CAN'T ride anymore, and although he's normally a horse who wants to put effort in, his try is...gone? As a note, its hard to explain in text but riding him, its not a health issue but very clearly a "attention span wall hitting" issue.
Now my question is, should I push him past this and make him continue to work, or cool him out and let him be done? I'm wondering because if I keep him going he may not focus but instead get mad and then stop learning, but if I let him be done for the day he won't build any stamina correct? So if the correct solution is to keep him working past his "I'M DONE" line, for how long? One more exercise, slowly increasing each individual time we work him past the "wall"? Answers? I hope this made sense.
Some notes: I am not "training" this horse alone, he has been to a real trainer twice (once for training once for a tuneup after a winter pretty much off).
He does not have discipline problems presently, he has not lashed out once he hits the "wall" I described he just loses interest, gets unsure, stops taking cues as easily/being as willing.
And an example of when this happened: after a walk trot lope trail ride that was probably oh an 2 hour, six mile trail ride. (p.s totally guessing about length )
Sorry for the length. Thank you guys.