FinnishLapphund
There's no cow on the ice
Very common problem, we do become used to doing things certain ways, changing habits is difficult and slipping back in the old habits is so easy, so accept that it might happen and if it does, don't allow it to lose your overall focus.
Try to remember to now and then think through what you really did with your dog that day/in a certain situation, for example : what did you think you said to your dog - what did the tone of your voice/your body language actually say? After more than 20 years as a dog owner, I still sometimes catch myself saying something, only to seconds later having to realize that the tone of my voice/my body language is saying something completely different than my words.
But maybe it is easier for me to remember to scrutinize my own behaviour because I know someone that is a good example on how not to do, she has a tendency to for example say "CALM DOWN!" in a tone that is actually so tense and agitated, that there is no wonder that the dogs only respond to what the tone of her voice is saying and since that is the opposite of what her words say, it has often ended with her saying "Why aren't they listening to me?"
So on the same theme, try to remember to take a few deep breaths before you react. For example, since you say that "He tries to get to other dogs when on his lead", I presume that you are like the majority of us humans, so after having had a few such experiences, if you're about to meet yet another dog out on a walk, you probably unknowingly become a little tense, but your dog doesn't realize that you become tense because you're anticipating his reaction, instead he's probably just seeing it as confirmation on that he's right to become tense around other dogs - after all - so do you!
I like the advice about writing down your goals and solutions, just don't forget to be realistic, after all, he's had several years of "training" up his skills in the bad habits, so as you presumably already know, changing it will take a little time
In the best of worlds it is of course ideal if everyone is working for the same goal, in the same way and at the same time. But if that is not the case, then in the beginning, it might lead to some confusion for the dog and it might lead to that it takes a little more time before new rules becomes established. However dogs are often quite adaptable and usually learn that different people have different demands, different levels for what the dog could get away with etc.
Good luck.