I've been persevering and doing quite well, but Luke was going stir-crazy with only having short training walks. Also if he's at the point of being out in front on a 6 foot training lead and another dog hoves into view, he goes bananas and I find it difficult to hold him, even using the "standing braced" technique we were taught at the seminar. So today he went back on his "Walkeezee" harness, so we could reach the park safely, and he had a really good run and play with his ball. Then we did some training, and he went back on the harness to come back. I feel this is a compromise but it's self-preservation for me, and more fun for him.

Its good to give yourself a break. Its a long term training thing and better to use the harness than be hurt or stressed. Glad you had a good time at the park.

Ok question is what do you do when he goes bananas? My suggestion would be to shorten his lead and stand in front of hin to 'demand' his attention and when you get it give praise and reward.  It may take some time but he will figure out what you want of him and to him any attention is a reward, so ignoring his bad behaviour and re-enforcing his good wiil, eventually, make him a better dog to live with.