Embarrassing Training Moment

I've started training two large St Bernards to go to the bathroom in one area on this fenced in estate. Owners know they are supposed to be training with me, but so far they are only following directions that I leave with them, instead of coming out and trying it with me. Any way, first day there I bring the dogs out one by one. First the older 175 pound dog, and then the younger 135 pound dog. The older one finishes first so he gets unhooked and gets cookies, and I go to my truck to get the prong collar to train him to be sent to the area. Just as I get there, the younger pup goes number two, so I close the door to my truck (I think I do any way), and I rush over to give the cookie and say good bathrooms when he is done. I look back, and I see Tango's face looking back at me from my truck window----later on it was too steamy to actually see his face. Seems I didn't close the door all the way, and the smarty pants figured out how to nudge it open and get in. I walk around to the back and open the door. "Come on Tango". Now this is the first day of training, and this is either dogs first day on a collar at all (he's still on just a flat at this point). Tango looks at me and stretches out full length along the back of my truck. Clearly he is enjoying Jazz's comfy and very fluffy doggie bed. Alrighty then, I take my trusty leash and hook it up to his collar (which I told the owners was to large), and begin to tug. I successfully pull the collar off of Tango's head. Tango does not look very impressed by me, and shows no signs of moving. This is the point where you are praying that the owners are not peeking out of the window to see how you are handling their very large dogs. I figure at this point, I will take Cash out and we will begin training. Jealous Tango will certaintly want to come out then. Bingo, thank God. I really was not relishing asking the owners to remove their dog from my vehicle. Now it's week 3, and Tango still looks longingly at my vehicle, and I shut that door but tight!!!