Hi dgibbo,
Firstly you are right a behaviourist or training classes should be your first port of call as we can not see what is going on here.
However, you need to look at this in a positive way which is he is not like this every day, which is a good sign :-) His behaviour can be corrected and it looks as though his behaviour is not based on him being a 'hyperactive' dog with all the problems that can bring.
From puppyhood calming behaviour should have continually been rewarded, when he sits nicely, comes when called, isn't too fussy and excitable, he should be praised and rewarded, whereas excitable behaviour should be completley ignored, you walk away, turn your back, or pop him in a time out for a few minutes, get used to using the words STOP! or CALM! This you need to put into place immediately if not doing so already, it all helps to keep your dog well behaved on his trips outside.
Yourself and a behaviourist need to look at why he is excitable outside some days but not others. Is he getting enough exercise day to day? Is he walked at different times, leading to a build up of excess energy? Is he given a different diet? Is he excitable at home before his walk? Is he allowed to build up to a frenzy whilst getting the lead ready?
When outside keep his focus on you rather than the rest of the outside world, play little training games, if he is not already in classes how about going for the KC bronze for starters? The two of you can have great fun and he is learning to obey and be a well behaved dog at the same time, does he enjoy playing ball, frizbee retrieve etc? Can you get him involved in playing with you more? He needs a good amount of exercise and it would be a good idea to divert his attention onto other things and in particular you, rather than chasing bikes, cats etc, otherwise a dog will make it's own entertainment.
Everything here is solvable, he just needs his attention diverting, and something else to occupy his mind, along with listening to you more, you can do all of those things, with help in classes or with a behaviourist. :-) Classes are more fun. :-)
By dgibbo
Date 20.04.09 05:51 UTC

Hi,
Thank you for your reply. My boy is now 5 years old, when he was small we went socialisation and then went to training classes. As time went on a couple of the people at class would say why have you brought him again he is so good. I haven't attended anywhere in the last two years. The reason I started lead walking him was his behaviour to other dogs. I used to have him off lead when I walked him up until he was 17 months old. The problem with him was that he is quite rough when he plays, he makes loads of noise and sounds as though he is very aggressive. When he would play with dogs, people with other dogs would get upset and I had to agree it did sound awful. The final issue was when I was out with him one day and a man with a chocolate labrador threatened to punch me. I have had two behaviourists around to my house but I actually have never been on a dog walk with them, I think this may be what I have to do. Also he did do his Bronze at training classes, but we didn't proceed with silver as we had to walk around the local streets and he wouldn't have been allowed to wear his halti, and I was worried about cats - and me being able to hold him if he saw the cat before I did. We got him at 8 weeks old, I would say from that day he has been hard work. We did have a dobermann before, but we didn't have children at that time, and I must admit I never considered him hard work at all. I love my dog very much, and would love to be able to enjoy him again.