I think you should start your own thread, instead of using SayiWont's thread, because you have some completely different issues going on.
What do you mean he "foundered in the neck"? Horses founder in their feet; not other body parts. Did you mean he has a cresty neck?
If he's stiff and lame, you need to get him to a vet. If he has indeed foundered, you are going to need to start taking care of his diet needs differently and possibly look into corrective shoeing. Yes, exercise is an important part of managing founder (laminitis) along with diet, but like I said, you need to have your horse checked by a vet who is familiar with laminitis.
Is that was it is? A cresty neck from eating so much grass during those raining times throughout the entire Spring? Riding in the rain isn't fun for either person horse or rider. The times I noticed him stiff was when he stands under a tree out of the summer sun and when I call him over, during the early mornings he's usually walking around, perhaps he'll feel a bit better when his feet get trimmed. As for horse shoes? He's never once had them on. I'll post up a new topic in a different thread. Thanks.