East, This will not get better by itself. In fact it will probably get worse.
So here goes:
Buy a prong collar or at the very least a choke chain.
Buy a heeling stick (I use Avery's available from gundogsupply)
Make a short lead (some call it a tag). Use 1/4 inch cord with a clip on one end. Make it in length so that if hold it at the very end, you can hook your thumb in your front pants pocket. For most dogs this is about 6-8inches.
Teach the dog to sit with the heeeling stick. A nice firm slap on the butt when you command "sit". At the same time lift up on the lead you are using (not the tag yet).
To teach to be steady:
If dog in on your left side. Hold tag line in right hand, pulling up on the lead with some pressure (called a taunt lead). You watch the dogs butt. Have heeling stick in your left hand. Have someone else throw a bumper. Remember the dogs job is to watch the bumper. Yours is to watch his butt. If he lifts his butt, command sit and slap him on the rump with the heeling stick. You are looking to get a good sting. Have your helper pick up the bumper (don't let the dog have it. This step is because of the age and previous experiences with your dog). Repeat until the dog sits calmly, then release on his name. Just let go of the tag lead.
The next step is a loose lead. No pressure on the lead, just some slack but still hold it like described above. You watch the dogs butt. If he moves slap with the heeling stick. Just hard enough for a good sting. If he moves have your helper pick up the bumper.
The you can move on to letting the lead dangle beside him. Caution: you might want to get him ecollar conditioned for this step.
The advantage of the short tag lead is that you can just let go of it and the dog can run with the lead dragging along between his legs or wherever.
This is not a one or two day process but will take a while, maybe several weeks since he has been accustomed to creeping or breaking. You are not going to intiminate the dog. It will be good for him in the long run and make him a better dog.
Evan gave you some good advise about getting on a training program. There are three that are talked about the most on this site. They are:
Total Retriever Training, 2ed. by Mike Lardy
Smartworks by Evan Graham
Fowldogs by Rick S.
There a lots of previous posts about these training programs. Yes, they are relatively expensive but cheap in the long run. If you can't afford one of them, I would suggest Mike Lardy's compilation of Retriever Journal articles, Vol 1. It is only $25. It describes the steadying process much more artifully and in more detail than I did with pictures, etc.
You can also do a search on this site and see some videos of Rowdy (by Pirate) becoming more steady gradually.
There are some previous threads about the advantages of using a prong collar. I would strongly suggest it for this dog. And for your ease in progressing. With some dogs a choke chain is more than adequate.
Hope this helps.