Hi Karl,
What you can do with your horse is first try to invite him to turn his neck sideways, by standing a litlle bit in front of his shoulder, looking in the same direction your horse does, and put your hand loosely on his nose, ask him to bend his neck towards you, giving him enough space for his head. Repeat several times. If this works both ways, try to do the same from the saddle, standing still and asking him to come towards your leg with his nose by lowering the rein on that side. Never force him, always ask him generously. Give him time to understand what's being asked of him and relax in the new situation.
Next step could be longlining in both directions and slowly shortening the inner side-rein.
For this please watch the lesson "Longlining for a horse that has been single-line lunged".
You could also have some amazing results with a chiropractor, assuming you find a real good one.
There's a lot you can do, use these exercises as a way to get to know your new horse better, giving him the chance to learn to trust you, too.
Miriam

Hi Miriam! Thank you for your reply!After revisiting Monty´s video I have started using my roundpen,and lounging without lines.There is no problem getting him to turrn his neck,as you suggested. It is only when he starts work, that he stiffens up his right side.

Two questions! Is it ok to take short trail rides after work in the roundpen,or should I save them for a while? The roundpen is only 13m in diameter,so the canter is a bit difficult for him. Do you think using the trot will reduce results?
Reg.
Karl

Hi Karl!
I think Miriam is right when saying a good chiropraktor might have amazing results.
Another idea I have would be that you should go to a chiropraktor as well and let him/her check your back, too. Sometimes the human vertebra is not in correct balance and we do not notice. Then we mount on our horse and have an inbalanced seat. This might also lead to an inbalanced horse having trouble with their own vertebra. And for the muscles of your horse I would advise you to go to a physiotherapeut, too.
Jasmin

Hi Karl,
From what you describe I 'd suggest you have a good check-up before riding him.
There could be a blockage in his pelvis, maybe the joint between pelvis and spine ( ileo-sacral joint), only a guess from this side of the internet.
There must be a reason for his stiffening, do try to find out, he'll thank you for it!
Miriam

Miriam has hit the nail on the head! Most riders and trainers do not teach their horses to double. To double your horse at a standstill and in the saddle start with a halter or (hackamore) an put the horses head around to touch your stirrup. Do this gently since most horse are not willing to do this the first time. Hold their head in that position for 10 or 15 seconds Let the head come back to neutral and then do the same thing on the other side. Do this 3 or 4 times
I can double my horse and still be riding in a straight line (lots of practice!) and go through this excise every time he is ridden. After awhile you will be able to just signal the horse using your reins. Doubling your horse does two things. First is builds flexibility into his neck muscles and second it builds balance in the horse. If your horse is not flexible on both sides of their body they cannot maintain a smooth equal gait. It my take a few weeks before you start to see a difference in your horse and how he strides out.

Cheers