Do you have any advice for me on marker training my dog? Do I leave out the verbal commands for now and just use the hand signals or gestures he knows?

Moose is a 2 1/2 year old mix, taken off death row at Animal Control. I've heard so many theories about what type of mix he is, that I've stopped guessing. He has already gone through two years of ongoing basic obedience training, and I consider him to be a well behaved/adjusted animal. I am currently starting him with marker training. Is there any advice you can provide me with to help me during this awkward time when the marker training and his previous training are overlapping/conflicting (e.g. The marker training method requires me to leave verbal commands out until a certain point in the dogs' training. Should I stop using those verbal commands for the time being, and use only the accompanying hand signals he knows? He knows "come" to come to me, and not using any one specific gesture I can get him to return to me non-verbally most of the time; however, when we are working together, he is in open space, occasionally with mild distractions, and I need to get him to return to me in a timely fashion, and the verbal command sometimes works best. Do I drop that command as well?) The information I have from you all is from scouring your site, and three of your films (Basic Obedience, Power of Food, Power of Markers). Any further thoughts you may have would be helpful. Thanks very much.

-David