Help with bucking.

[showjumper]

I,ve had duke on loan for about 5 weeks now and his bucking is getting worse. To start with, it was jst a little kick as he got into canter which is normal for him if he,s not cantered for a while, but now he starts really bucking when I put my leg on. He is a 7 yr old cob x trotter and finds canter difficult, he never does more than a few strides then he collapses into a walk and no amount of kicking can get him moving. Last week I managed to get a good canter out of him and it,s since then the bucking has started, even while walking. He has had a full check but nothing can be found, but he has started to get a clicky hock, which is going to be checked. I have noticed the only time he plays up is when it,s windy, and he is a bossy horse, so i,m wondering if he,s jst trying to get his own way. I took him on a hack yesterday with another horse and he started bucking down the road when I asked for trot. How can I stop him?

Edt. Forgot to add, he doesn,t do it on the lunge.

[Kaliska]

Have you had your vet give him a full health check and back check?

[Snipper]

Have you had your saddle checked? Might be why he only does it with a rider on? Also, what do you do when he bucks, do you keep riding him forward or get worried and back off?