My experience with Ari.
1 - jumping. It took 2 days to correct. Inside - every time he jumps on anyone, everyone leaves the room for 10-15 sec. Outside during walks - every time he jumps on me, the walk and the game stops, I become a tree, no movement, no eye contact, no talking to him, no reaction of any kind. When he comes down - we move on.
2 - stopping suddenly in the middle of the walk, changing directions - if there is a rabbit or a squirrel nearby, he will want to go after it. If we are walking through the woods - its always moving in different directions, to catch all the scents around. In general - he's has gotten much better on the leash (he is 15 months), it took months and months of work, and will never be perfect. Every walk is rolling the dice, it's just we have nice calm walks much more often now. My personal take on this - he will not be the one to always stay by my side during the walk, he will be wondering around, sniffing and sticking his nose everywhere, and I am fine with that.
We take walks in town (people, cars, etc), and we take walks in the nature park. In town he stays by my side. On a trail in the park he would be all over the place. So I put him on a 30 ft training leash when we go to the park - this way he can do his thing (left, right, forward, backward, sniffing everything) without me having to do the same thing

. In all his excitement and sniffing and exploring, he rarely ventures beyond 30 ft, and when he does - a gentle pull and calling him back does the trick.
To be honest, none of this really bothers me. I like seeing him enjoying his walks, and if it's a "stop and go" kind, then so be it. We jog now too, which makes things better, but it's still usually a "stop and go", not at all steady moving in one direction at constant speed

re dog parks.... At some point we had to switch things around (walk first to burn some energy off, then dog park). It depends on the dogs to some extend, but Ari can be a bit of a bully at the dog park, which in turn can provoke another dog to attack him. So usually we go for a 40 min to an hour walk, then dog park. Ari is a big, strong, adolescent bully, unneutered which doesn't help.
If we had a good playmate for Ari, I would just stop dog park visits. I don't want him to make other, more timid dogs uncomfortable, and don't want to risk one of those dogs reacting aggressively and attacking him.. But he needs socialization, so we go, and I watch him very closely ready to step in when things become a little too tense. But, this is also getting better, perhaps he is starting to grow out of his "bully" stage?
Bottom line here for me - I gave up on the idea of nice walks in a straight line and steady speed, where the dog follows the human. I can have this during a city walk, but not in the nature park, which he enjoys the most.. And this is perfectly fine with me. But what's so wrong with dog changing directions?? As someone said earlier - "whose walk is this anyway??"

cheers
Eugene