I want to start marker training, which DVDs should I get? And what can I be doing until I get them?

I ran across your article online about your thoughts on marker training. I was taught to train by only correcting bad behaviors in the early 90s. Yankin and crankin. It has worked well for me in obedience training my dogs over the years. Your article however has caused me to rethink my approach. I have 2 german shephard puppy?litter mates male and female. I got them at 4 months. They are now 6 months.?I walk them and train them every day. As a side note, I train and walk them separately. They also sleep separately in an attempt at having them connect with my wife and me and not just each other. So far it's going pretty well. My question for you is of all the DVDs you offer, like The Power of Marker Training or playing tug or training with food. Which single one or series would you recommend? One more point is, what should I do regarding my training until I can start applying the marker method? I don't want to be in a situation where I have to spend weeks or months undoing something that doesn't fit. I also will continue walking them and with out correction at this point the 60 pound male will be dislocating my shoulder. Anyway my wife and I are 50 and are committed to having solid companion dogs for many years to come and are willing to do what it takes. I'm sorry for the length of this message. I am looking forward to advise and suggestions.

Thanks,
Tim