Sorry for late reply, no he wasn't trying to mount him.
He stood over him as the dog was small at fits under him.
When he does this. I immediately pull him off.
Since writing to you, I have been practicing the above and am seeing progress.
I have been using a collar instead of harness and have been getting a better response.
Tomorrow we also start obedience training in a group environment, so hoping this will help with the over excitement.
When he reaches the end of lead I have been calling turn around or sometimes I just stop and he knows to come back to my Side.
This is working great, you can see his mind ticking, and his walking has improved, when he sees something exciting I just keep stopping turn around and move closer when calm. If his not calm we don't progress.