
I dont know if you use mats in the ring, but this is what I do with a pup that is nervous in the ring.
I got some of that stuff you put on tables to things (like tablecloths) dont slide. It comes in a square mat, that feels kinda like the top of a grooming table, or mat. I first just put one down, then gave treats if the pup stood on it. You may have to use a couple to start out with, since you have a bigger dog (I show min pins)
Then once the dog is confortable, on just the one mat, then I go to three, where the dog has to take steps to move over it. I stand on the other side, and call come! and guide the dog over with treats.
You may be thinking, why use the word come, if you got to move beside the dog in the ring. The answer is this, you want the dog to forget about the mats, so if it is doing something it already knows, then it is easier.
Then you put the squares down the hallway, and say heel. Walk the dog up and down them. Soon, once the dog is moving ok in a heel, add some speed, eventually going up to the speed you show in the ring.
Some dogs dont like the feel of the mats, and thats why they stop moving in the ring. I have used this, and it works for me.
It does take a while though, with my pin, it took almost a month before she would walk on the mats. Then I took her to a show, and she worked fine.
Sometimes also, if you are stressed, the dog feels that even though you are trying so hard to hide it. The dog will react this way, especially if you are anticipating trouble. Go in thinking, who cares if I get dumped? I know my dog is the best. Then you and your dog will feel good, and it may just be that.
Hope this helps!