Okay. I will try to answer you section by section -- hopefully to make this easier. =P
I have used the crop and the spurs ( only little itsy bitsy tiny nubs you can barely see, and he did respond ok to them. I prefer not to use extra equipment if don't have to though. I have sed the crop on him every now and again, and he go the point and would go faster, but I worry that he might have grown to dislike it, because when I did use it, it was when I was short tempred and angry, and I did whack good ( 4 or 5 times in a row), when he got a little obstinant , because I was busy being a big time b*tch and dumb a**. Sometimes I hate myself, looking back....
It's always a good thing not to use extra stuff more than you need it. It's really just there to be a back-up for when your leg isn't enough.
For the most part you have to be careful with crops and spurs, but I know from experience that horses can be re-sensitized to pretty much whatever. I used to ride a horse whose old owner would hit him with a crop out of frustration. He was at the point that he didn't listen easily to anything. It took very constant use of asking nicely with your leg and then whacking him to make him move. Before I stopped riding him he had got to the point where he would do everything but canter immediately when you gave him a little squeeze with your legs, and if you asked nicely a few times he'd even canter off just your legs. (He still had a long way to go, but it was a major improvement.)
My trainer always taught me it was "Ask, tell, NOW." Basically squeeze nicely with your legs, squeeze harder with your legs, and then smack. Every horse I worked with with her rapidly learned to move off your leg. I know it might seem a bit harsh, but it worked, and in the end it's nicer than repeatedly kicking or whatever. (Just sharing all my knowledge, and you figure out what works best for you and Solo in this sort of case since I don't really know how well he responds. And hopefully this will be helpful when he gets obstinate. The horse I was talking about earlier was VERY stubborn. And he learned very well that it was easier to respond than not to.)
AH AHA! Ground work and lunging! Now THERE is something we know well! If there is one thing we do well in, it's ground work and lunging! I nick named him "Lunge King"? Because he's so good at it- and I worked hard to make him that way ( and trust me, he was an utter brat when I first got him). LOL He's fantastic on th lunge.
Good to know. Have you ever worked with asking him to bend on the lunge?
Yes, I have access to a 50 foot roundpen. Solo is 15.3 and still growing. I traind him in a 60-foot pen, but I'm worried a 50ft will be too small ( I will be moving him to my currewnt barn soon... he's still at the old one learning to trailer)?
If you think he's too big for it then just go with your judgement. And if he knows how to lunge well it doesn't really matter.
You mean slow or speed his current gait before moving into the one I'm asking for? For the most part. Sometimes he does it right away , if he's listening and feeling compliant that day.
So what exactly does he do? Say you're asking for the walk from the trot? Does he usually slow down the trot before walking, or just walk? Same for trot to canter. Does he speed up his trot before cantering, or just canter?
Will do serpentines and such. Ye, he does allow his shoulder to fall in. I was told to fix this by only allowing so much give on the outside rein to say, "you turn, but only so far". Is this correct?
Not the same wording I've heard (but jeez there are so many), but yes, same principal. Another thing you can try is practice leg yields. If Solo gets really good at leg yields you can eventually teach him to pick up his shoulder with your inside leg and outside rein, and pretty much eventually entirely off your inside leg.
Also, a bit of info I can't remeber if I;ve given or not- he pulled a muscle in his back at least 6 months ago, and it does not appear to be givin him any problems, but I wonder if he'll be stiff for a while before figuring out it's not going to hurt when I ride again?
Probably. He might also be stiff because his muscles aren't as strong as they used to be. But my trainer always taught me that even when the horse is stiff you have to teach them what is comfortable, even if that means really pushing for a bend for a while. They do realize quickly that bending is more comfortable than traveling hollowly. It can take a while before they bend fairly constantly, though, because it requires a fair amount of muscle.
Also, be sure that once he starts bending (tracking up with his hind legs, rounding his back and dropping his head, etc.) be sure to give him a release. Basically (in the beginning) everytime he bends (does the above listed) loosen your rein as far as you can (I don't know if you have to keep it at a certain length with him or whatever) so that he has the opportunity to stretch his neck. What you're aiming for is so that after he bends when you release for him to drop his nose to the ground and stretch. But make sure not to let him grab at the bit and yank his head to the ground. If he tries that, hang on (don't pull back, just hold), so that he runs into the bit. He'll learn fast not to do that.
Once he gets a bit more advanced with the bending you'll start only giving a little bit on the inside rein, and eventually to the point where he will essentially give himself his own release by bending properly, and you will give him a release in between exercises and not during them. (Basically, say when he starts bending now, you're trotting, he bends, you give him a release, and then slowly -- using stride -- you gather the reins back up and ask again.)
Just one last thing, what sort of work did you do with him right after he healed when you started working with him again? How long have you been working with him/riding him since he healed? How long did you work with/ride him before that?