I think your last post is on track and should help a lot.
So many things happen (and can go wrong) in water "obstacles" - not just while driving either. The backup thing - well - the only thing I can say is to keep working on him until a touch of your whip causes any backing (good, asked for or "mindless") to stop and get at least a stand and then hopefully will step out or forward when asked again. Then main thing is to get the "mindless" backing stopped - preferably before you back into something or jack up your cart.
A couple of mine when through this - both were affected when turning to the left in shafts. They'd both (2 years apart) would all of a sudden act like they'd been attacked by the shaft when they were asked to turn to the left and they'd throw their heads and then do a combo of leaping up/down (partial rearing) and backing - jamming themselves in a "curve" in the shafts but moving their bodies and the cart to the right. With both ponies, it took many times of having a header take a hold of them and lead them thru the curve/turn to the left and forward. Neither one ever went thru this while ground driving or while pulling a drag (no shafts).
The one mare, long after I thought we'd gotten past this as a single, suddenly did it while hitched as a pair out on a trail drive. I DID have a friend with me (thank goodness) - because we ended up needing help. When Koalah started her jam, back and leap to the right (she was on the left side of the pair) - she pushed her partner with her as well as her foal who was also attached to her. BUT - when she pushed them all to the right while trying to back up - we left the clear running water of the stream that was on a "packed" & graveled fording spot and literally "fell" off of the trail into ... a black hole. Then, off balance and still leaping around, the fore cart I was driving had a wheel jammed up against a large tree stump that was also in that "black hole". The mares finally quieted down - trembling and big eyed. Koalah was actually mired up to her elbows in front, her pendulous belly below the water line and her hocks behind. I, too, remember being "big eyed" with shock and maybe even a bit of fear as well (had NO IDEA what was in that muck and if the girls' legs that were heavily mired were OK and OMG - what about snakes??). That cart was well over 200 lbs and was off balance/off kilter tilted sideways and also mired down on the right side... The only reason the girls had come to a stop and were now mired - the cart wouldn't go anywhere. Couldn't go backwards anymore, tilted and stuck...
Once I took a deep breath, I tied the lines to both mares snugly back to the bar at the front of the cart and scrambled off the cart onto the packed area of the water fording. I was able to reach the filly's lead and untie her - she was the least mired and I was able to turn her head to me and encourage her to step back up to the packed path in shallow, now not so clear, water. Led her out of the water and tied her to a tree in front of the pair and on a dry spot of the path. By now, Vicki also has her pair turned around, stopped and tied to a tree (together). and she joins me and is wondering (aloud) how we are going to get this mess worked out... I don't remember anymore the exact order - think I got back into the cart and leaned way over the front to the girls butts and unhooked the tie hooking their haunches together. Then unhitched the farm traces, too. Then out of the cart and to the front of them... Seem to recall only having one lead rope - don't know why- that is highly unusual. Koalah lets out a groan at this point and completely lays down (still hooked as a team by the driving lines and at the front of the tongue to her collar and Bit fights against the drag - not wanting to go down and scrambles about. I wait (I think?) - then go in front of them (UGH!!) and unhook both of them from the tongue - then undid the lines hooking Bit's bridle - letting the snaps slide clear. Think Vicki tossed a lead to me and I hooked it to her halter and we turned to the right - back and around - to firm ground. Bit is out - though trembling. I see no blood, rips or tears, she's moving solid and square - not limping. She is also tied up - to a tree that is on the backside of the water (didn't occur to us that that was WRONG place to be!!).
Then back to Koalah. She's no longer attached to the tongue and the lines are loose (?don't remember how - they ARE still tied to the cart)... She is still laying down - I don't know if her legs are caught in a branch, log or hole - had she been bitten by something??. Honestly - part of my mind was slavvering and screaming. I wanted nothing to do with the muck that she was mired down in but I knew that we didn't have a choice - I wanted/needed her out of that "hole". My cell phone had no service - so help wasn't coming & we were still on our own. I must have braved the muck - 'cuz I remember going to her RIGHT side, feeling down the right leg and lifting/pulling it free of the mud. Took some time to move around to the front of her and thank goodness she didn't struggle then 'cuz if she'd have hit me - I'd have broken as I was fighting the sucking mud now, too! Undid the lines and tossed them back to the cart. Kept moving to the left in front of her and got her left fore leg free and yelled/slapped her on the neck and she was struggling up/out of the sucking mess (and now it stinks to high kingdom come too!) got her up on the "clearer" fording spot and she splash around funny for a moment or two - then walked out normally. She drops her head down to the ground - her sides are heaving but she doesn't appear injured. Just stress exhaustion and struggling. A lot of the mud on them ran off when led them thru the water and out. She is tied up with Bell.
The cart - was an issue. It is heavy and inanimate. We ended up turning the foal loose & tying Bit and Koalah with the same lead rope - so that we could use the two together to help pull the cart out... We used a small tree that was dead next to the trail as a wedge to push on the cart's right wheel - to get it unmired and uncaught where it was hung up on the stump. I know that afterwords, vicki was ready to kill me for having the larger/heavier cart (haflinger sized) and we were both soaked in sweat, water and slimy, stinky MUD with our own sides heaving with exertion. It wasn't until after i re-hitched the mares that I realized that we still had to go thru/cross the ford - thru water that was not yet running clear. OMG - what was I thinking (O, that's right - wasn't!).
Here is a pic - after re-hitching them
The cart/tongue doesn't even look muddy! Trust me, it was - took forever to get it clean when I got home.
Guess what? Koalah DID NOT get "silly" again - she dropped her head, sniffed at the water and then both her and Bit went on thru. Vicki untied her pair and we slowly finished out our drive (and were able to shorten it some by taking a different path - going back to trailers sooner). The mares were still kinda "draggy" when we got home - I know that I gave them both full, soapy baths (they smelled BAD - so did I). I didn't feed them right away - instead turning them out to pasture while I went in and showered the muck off of me and redressed in dry clothes (had to wear slip on shoes - nasty paddock boots went into washer - took several days to finally dry out).
I did go back to ground driving Koalah - both single and as a pair. But never had a problem with that again. So back to hitching - both single and pair - never again did she do that "back up/ rear/swing to the right" thing...
I don't recommend this type of training if it can be avoided - but it worked in this situation :-
So... I do recommend following Marsha's advice. It does work (I've done that again and again, too).
LOVED how you handled your guy at the driving event where the woman was "crazy"... Good for you!