I have a harness that attaches to the seatbelt for our 11mo puppy; problem is that now he cannot fit on any of the vehicle seats. I have to fold one of the captains chairs down into the floor (I LOVE the Stow N Go feature of my Grand Caravan!!!) to give him room. So is it safe to attach a lead to the caribeaner (sp?) on the harness and find a spot on the floor to tether it to (front passenger chair leg, etc), or is there some special way to restrain a 135# and quickly growing dog? His projected weight is between 220-250lbs, based on lineage and bone structure, if that helps.